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Why does a 'for' loop behave differently when migrating VB.NET code to C#?
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up vote
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I'm in the process of migrating a project from Visual Basic to C# and I've had to change how a for loop being used is declared.
In VB.NET the for loop is declared below:
Dim stringValue As String = "42"
For i As Integer = 1 To 10 - stringValue.Length
stringValue = stringValue & " " & CStr(i)
Console.WriteLine(stringValue)
Next
Which outputs:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
In C# the for loop is declared below:
string stringValue = "42";
for (int i = 1; i <= 10 - stringValue.Length; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
This obviously isn't correct so I had to change the code ever so slightly and included an integer variable that would hold the length of the string.
Please see the code below:
string stringValue = "42";
int stringValueLength = stringValue.Length;
for (int i = 1; i <= 10 - stringValueLength; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
Now my question resolves around how Visual Basic differs to C# in terms of Visual Basic using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes. Whereas in C# if I use the stringValue.Length in the for loop condition it changes the initial string value each time the loop occurs. Why is this?
c# vb.net loops for-loop
edited 22 mins ago
Peter Mortensen
13.1k1983111
asked 2 days ago
slee423
5671422
 |Â
show 6 more comments
up vote
61
down vote
favorite
I'm in the process of migrating a project from Visual Basic to C# and I've had to change how a for loop being used is declared.
In VB.NET the for loop is declared below:
Dim stringValue As String = "42"
For i As Integer = 1 To 10 - stringValue.Length
stringValue = stringValue & " " & CStr(i)
Console.WriteLine(stringValue)
Next
Which outputs:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
In C# the for loop is declared below:
string stringValue = "42";
for (int i = 1; i <= 10 - stringValue.Length; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
This obviously isn't correct so I had to change the code ever so slightly and included an integer variable that would hold the length of the string.
Please see the code below:
string stringValue = "42";
int stringValueLength = stringValue.Length;
for (int i = 1; i <= 10 - stringValueLength; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
Now my question resolves around how Visual Basic differs to C# in terms of Visual Basic using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes. Whereas in C# if I use the stringValue.Length in the for loop condition it changes the initial string value each time the loop occurs. Why is this?
c# vb.net loops for-loop
edited 22 mins ago
Peter Mortensen
13.1k1983111
asked 2 days ago
slee423
5671422
5
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
37
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
9
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
32
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
23
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago
 |Â
show 6 more comments
up vote
61
down vote
favorite
up vote
61
down vote
favorite
I'm in the process of migrating a project from Visual Basic to C# and I've had to change how a for loop being used is declared.
In VB.NET the for loop is declared below:
Dim stringValue As String = "42"
For i As Integer = 1 To 10 - stringValue.Length
stringValue = stringValue & " " & CStr(i)
Console.WriteLine(stringValue)
Next
Which outputs:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
In C# the for loop is declared below:
string stringValue = "42";
for (int i = 1; i <= 10 - stringValue.Length; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
This obviously isn't correct so I had to change the code ever so slightly and included an integer variable that would hold the length of the string.
Please see the code below:
string stringValue = "42";
int stringValueLength = stringValue.Length;
for (int i = 1; i <= 10 - stringValueLength; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
Now my question resolves around how Visual Basic differs to C# in terms of Visual Basic using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes. Whereas in C# if I use the stringValue.Length in the for loop condition it changes the initial string value each time the loop occurs. Why is this?
c# vb.net loops for-loop
edited 22 mins ago
Peter Mortensen
13.1k1983111
asked 2 days ago
slee423
5671422
I'm in the process of migrating a project from Visual Basic to C# and I've had to change how a for loop being used is declared.
In VB.NET the for loop is declared below:
Dim stringValue As String = "42"
For i As Integer = 1 To 10 - stringValue.Length
stringValue = stringValue & " " & CStr(i)
Console.WriteLine(stringValue)
Next
Which outputs:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
In C# the for loop is declared below:
string stringValue = "42";
for (int i = 1; i <= 10 - stringValue.Length; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
This obviously isn't correct so I had to change the code ever so slightly and included an integer variable that would hold the length of the string.
Please see the code below:
string stringValue = "42";
int stringValueLength = stringValue.Length;
for (int i = 1; i <= 10 - stringValueLength; i ++)
stringValue = stringValue + " " + i.ToString();
Console.WriteLine(stringValue);
And the output:
42 1
42 1 2
42 1 2 3
42 1 2 3 4
42 1 2 3 4 5
42 1 2 3 4 5 6
42 1 2 3 4 5 6 7
42 1 2 3 4 5 6 7 8
Now my question resolves around how Visual Basic differs to C# in terms of Visual Basic using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes. Whereas in C# if I use the stringValue.Length in the for loop condition it changes the initial string value each time the loop occurs. Why is this?
c# vb.net loops for-loop
c# vb.net loops for-loop
edited 22 mins ago
Peter Mortensen
13.1k1983111
asked 2 days ago
slee423
5671422
edited 22 mins ago
Peter Mortensen
13.1k1983111
asked 2 days ago
slee423
5671422
edited 22 mins ago
Peter Mortensen
13.1k1983111
edited 22 mins ago
Peter Mortensen
13.1k1983111
edited 22 mins ago
Peter Mortensen
13.1k1983111
13.1k1983111
asked 2 days ago
slee423
5671422
asked 2 days ago
slee423
5671422
asked 2 days ago
slee423
5671422
5671422
5
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
37
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
9
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
32
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
23
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago
 |Â
show 6 more comments
5
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
37
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
9
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
32
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
23
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago
5
5
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
37
37
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
9
9
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
32
32
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
23
23
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago
 |Â
show 6 more comments
5 Answers
5
active
oldest
votes
up vote
91
down vote
accepted
In C#, the loop boundary condition is evaluated on each iteration. In VB.NET, it is only evaluated on entry to the loop.
So, in the C# version in the question, because the length of stringValue is being changed in the loop, the final loop variable value will be changed.
In VB.NET, the final condition is inclusive, so you would use <= instead of < in C#.
answered 2 days ago
Andrew Morton
14.4k43047
Thanks for the reply. I now realise that using<=allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and inVBI didn't have to. I'm going to update my question to show the same output.
– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length ofstringValueis being changed in the loop, the final loop variable value will be changed.
– Andrew Morton
2 days ago
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
add a comment |Â
up vote
19
down vote
Now my question resolves around how VB differs to C# in terms of VB using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes.
According to the VB.NET documentation:
If you change the value of
counterwhile inside a loop, your code might be more difficult to read and debug. Changing the value ofstart,end, orstepdoesn't affect the iteration values that were determined when the loop was first entered.
So, the value of To 10 - stringValue.Length is evaluated once and reused until the loops exit.
However, look at c#'s for statement
If the
for_conditionis not present or if the evaluation yieldstrue, control is transferred to the embedded statement. When and if control reaches the end point of the embedded statement (possibly from execution of a continue statement), the expressions of thefor_iterator, if any, are evaluated in sequence, and then another iteration is performed, starting with evaluation of thefor_conditionin the step above.
Which basically means that the condition ; i <= 10 - stringValueLength; is evaluated again each time.
So, as you saw, if you want to replicate the code, you need to declare the final counter in c# before starting the loop.
answered 2 days ago
Camilo Terevinto
16.3k63160
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
add a comment |Â
up vote
9
down vote
In order to make the example more understandable, I will convert both for loops into C# while loops.
VB.NET
string stringValue = "42";
int min = 1;
int max = 10 - stringValue.Length;
int i = min;
while (i <= max)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
C#
string stringValue = "42";
int i = 1;
while (i <= 10 - stringValue.Length)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
The difference is then:
VB.NET caches the maximum value for
i, but C# recomputes it every time.
edited 20 hours ago
camerondm9
485715
answered 2 days ago
Maxime Recuerda
26213
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
It helped me to understand thefor loopsat my begins, I think they are much more understandable. This is why I 'translated' the examples inwhile loops, to help understanding.
– Maxime Recuerda
2 days ago
add a comment |Â
up vote
5
down vote
Because the for in VB is a different semantic than the for in C# (or any other C-like language)
In VB, the for statement is specifically incrementing a counter from one value to another.
In C, C++, C#, etc., the for statement simply evaluates three expressions:
- The first expression is customarily an initialization
- The second expression is evaluated at the start of each iteration to determine whether the terminal condition has been met
- The third expression is evaluated at the end of each iteration, which is customarily an incrementer.
In VB, you must supply a numeric variable which can be tested against a terminal value and incremented on each iteration
In C, C++, C#, etc., the three expressions are minimally constrained; the conditional expression must evaluate to a true/false (or integer zero/non-zero in C, C++). You don't need to perform an initialization at all, you can iterate any type over any range of values, iterate a pointer or reference over a complex structure, or not iterate anything at all.
So, in C#, etc., the condition expression must be fully evaluated on each iteration, but in VB, the terminal value of the iterator must be evaluated at the beginning, and need not be evaluated again.
answered 2 days ago
C Robinson
1037
add a comment |Â
up vote
-3
down vote
I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to.
In VB, type the declaration is optional depending on the existence of the Option Explicit setting in the file.
answered yesterday
Terry Carmen
2,0571717
The integer variable they’re referring to isstringValueLength.
– Ry-♦
yesterday
add a comment |Â
5 Answers
5
active
oldest
votes
5 Answers
5
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
91
down vote
accepted
In C#, the loop boundary condition is evaluated on each iteration. In VB.NET, it is only evaluated on entry to the loop.
So, in the C# version in the question, because the length of stringValue is being changed in the loop, the final loop variable value will be changed.
In VB.NET, the final condition is inclusive, so you would use <= instead of < in C#.
answered 2 days ago
Andrew Morton
14.4k43047
Thanks for the reply. I now realise that using<=allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and inVBI didn't have to. I'm going to update my question to show the same output.
– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length ofstringValueis being changed in the loop, the final loop variable value will be changed.
– Andrew Morton
2 days ago
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
add a comment |Â
up vote
91
down vote
accepted
In C#, the loop boundary condition is evaluated on each iteration. In VB.NET, it is only evaluated on entry to the loop.
So, in the C# version in the question, because the length of stringValue is being changed in the loop, the final loop variable value will be changed.
In VB.NET, the final condition is inclusive, so you would use <= instead of < in C#.
answered 2 days ago
Andrew Morton
14.4k43047
Thanks for the reply. I now realise that using<=allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and inVBI didn't have to. I'm going to update my question to show the same output.
– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length ofstringValueis being changed in the loop, the final loop variable value will be changed.
– Andrew Morton
2 days ago
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
add a comment |Â
up vote
91
down vote
accepted
up vote
91
down vote
accepted
In C#, the loop boundary condition is evaluated on each iteration. In VB.NET, it is only evaluated on entry to the loop.
So, in the C# version in the question, because the length of stringValue is being changed in the loop, the final loop variable value will be changed.
In VB.NET, the final condition is inclusive, so you would use <= instead of < in C#.
answered 2 days ago
Andrew Morton
14.4k43047
In C#, the loop boundary condition is evaluated on each iteration. In VB.NET, it is only evaluated on entry to the loop.
So, in the C# version in the question, because the length of stringValue is being changed in the loop, the final loop variable value will be changed.
In VB.NET, the final condition is inclusive, so you would use <= instead of < in C#.
answered 2 days ago
Andrew Morton
14.4k43047
edited 2 days ago
answered 2 days ago
Andrew Morton
14.4k43047
answered 2 days ago
Andrew Morton
14.4k43047
answered 2 days ago
Andrew Morton
14.4k43047
14.4k43047
Thanks for the reply. I now realise that using<=allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and inVBI didn't have to. I'm going to update my question to show the same output.
– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length ofstringValueis being changed in the loop, the final loop variable value will be changed.
– Andrew Morton
2 days ago
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
add a comment |Â
Thanks for the reply. I now realise that using<=allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and inVBI didn't have to. I'm going to update my question to show the same output.
– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length ofstringValueis being changed in the loop, the final loop variable value will be changed.
– Andrew Morton
2 days ago
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
Thanks for the reply. I now realise that using
<= allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to. I'm going to update my question to show the same output.– slee423
2 days ago
Thanks for the reply. I now realise that using
<= allows me to iterate and have the same output as the VB code. However, I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to. I'm going to update my question to show the same output.– slee423
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length of
stringValue is being changed in the loop, the final loop variable value will be changed.– Andrew Morton
2 days ago
@slee423 The reason is given in the first sentence of my answer. Because the length of
stringValue is being changed in the loop, the final loop variable value will be changed.– Andrew Morton
2 days ago
1
1
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
apologies, thanks for that answer. And thanks for elaborating it in more detail for me.
– slee423
2 days ago
1
1
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
@slee423 I added that into the answer as it does indeed clarify it.
– Andrew Morton
2 days ago
add a comment |Â
up vote
19
down vote
Now my question resolves around how VB differs to C# in terms of VB using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes.
According to the VB.NET documentation:
If you change the value of
counterwhile inside a loop, your code might be more difficult to read and debug. Changing the value ofstart,end, orstepdoesn't affect the iteration values that were determined when the loop was first entered.
So, the value of To 10 - stringValue.Length is evaluated once and reused until the loops exit.
However, look at c#'s for statement
If the
for_conditionis not present or if the evaluation yieldstrue, control is transferred to the embedded statement. When and if control reaches the end point of the embedded statement (possibly from execution of a continue statement), the expressions of thefor_iterator, if any, are evaluated in sequence, and then another iteration is performed, starting with evaluation of thefor_conditionin the step above.
Which basically means that the condition ; i <= 10 - stringValueLength; is evaluated again each time.
So, as you saw, if you want to replicate the code, you need to declare the final counter in c# before starting the loop.
answered 2 days ago
Camilo Terevinto
16.3k63160
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
add a comment |Â
up vote
19
down vote
Now my question resolves around how VB differs to C# in terms of VB using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes.
According to the VB.NET documentation:
If you change the value of
counterwhile inside a loop, your code might be more difficult to read and debug. Changing the value ofstart,end, orstepdoesn't affect the iteration values that were determined when the loop was first entered.
So, the value of To 10 - stringValue.Length is evaluated once and reused until the loops exit.
However, look at c#'s for statement
If the
for_conditionis not present or if the evaluation yieldstrue, control is transferred to the embedded statement. When and if control reaches the end point of the embedded statement (possibly from execution of a continue statement), the expressions of thefor_iterator, if any, are evaluated in sequence, and then another iteration is performed, starting with evaluation of thefor_conditionin the step above.
Which basically means that the condition ; i <= 10 - stringValueLength; is evaluated again each time.
So, as you saw, if you want to replicate the code, you need to declare the final counter in c# before starting the loop.
answered 2 days ago
Camilo Terevinto
16.3k63160
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
add a comment |Â
up vote
19
down vote
up vote
19
down vote
Now my question resolves around how VB differs to C# in terms of VB using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes.
According to the VB.NET documentation:
If you change the value of
counterwhile inside a loop, your code might be more difficult to read and debug. Changing the value ofstart,end, orstepdoesn't affect the iteration values that were determined when the loop was first entered.
So, the value of To 10 - stringValue.Length is evaluated once and reused until the loops exit.
However, look at c#'s for statement
If the
for_conditionis not present or if the evaluation yieldstrue, control is transferred to the embedded statement. When and if control reaches the end point of the embedded statement (possibly from execution of a continue statement), the expressions of thefor_iterator, if any, are evaluated in sequence, and then another iteration is performed, starting with evaluation of thefor_conditionin the step above.
Which basically means that the condition ; i <= 10 - stringValueLength; is evaluated again each time.
So, as you saw, if you want to replicate the code, you need to declare the final counter in c# before starting the loop.
answered 2 days ago
Camilo Terevinto
16.3k63160
Now my question resolves around how VB differs to C# in terms of VB using the stringValue.Length condition in the for loop even though each time the loop occurs the length of the string changes.
According to the VB.NET documentation:
If you change the value of
counterwhile inside a loop, your code might be more difficult to read and debug. Changing the value ofstart,end, orstepdoesn't affect the iteration values that were determined when the loop was first entered.
So, the value of To 10 - stringValue.Length is evaluated once and reused until the loops exit.
However, look at c#'s for statement
If the
for_conditionis not present or if the evaluation yieldstrue, control is transferred to the embedded statement. When and if control reaches the end point of the embedded statement (possibly from execution of a continue statement), the expressions of thefor_iterator, if any, are evaluated in sequence, and then another iteration is performed, starting with evaluation of thefor_conditionin the step above.
Which basically means that the condition ; i <= 10 - stringValueLength; is evaluated again each time.
So, as you saw, if you want to replicate the code, you need to declare the final counter in c# before starting the loop.
answered 2 days ago
Camilo Terevinto
16.3k63160
answered 2 days ago
Camilo Terevinto
16.3k63160
answered 2 days ago
Camilo Terevinto
16.3k63160
answered 2 days ago
Camilo Terevinto
16.3k63160
16.3k63160
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
add a comment |Â
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
4
4
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
The end condition evaluation has the corollary that even if it doesn't vary but it is expensive to calculate, then it should be calculated just once before the loop.
– Andrew Morton
2 days ago
add a comment |Â
up vote
9
down vote
In order to make the example more understandable, I will convert both for loops into C# while loops.
VB.NET
string stringValue = "42";
int min = 1;
int max = 10 - stringValue.Length;
int i = min;
while (i <= max)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
C#
string stringValue = "42";
int i = 1;
while (i <= 10 - stringValue.Length)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
The difference is then:
VB.NET caches the maximum value for
i, but C# recomputes it every time.
edited 20 hours ago
camerondm9
485715
answered 2 days ago
Maxime Recuerda
26213
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
It helped me to understand thefor loopsat my begins, I think they are much more understandable. This is why I 'translated' the examples inwhile loops, to help understanding.
– Maxime Recuerda
2 days ago
add a comment |Â
up vote
9
down vote
In order to make the example more understandable, I will convert both for loops into C# while loops.
VB.NET
string stringValue = "42";
int min = 1;
int max = 10 - stringValue.Length;
int i = min;
while (i <= max)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
C#
string stringValue = "42";
int i = 1;
while (i <= 10 - stringValue.Length)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
The difference is then:
VB.NET caches the maximum value for
i, but C# recomputes it every time.
edited 20 hours ago
camerondm9
485715
answered 2 days ago
Maxime Recuerda
26213
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
It helped me to understand thefor loopsat my begins, I think they are much more understandable. This is why I 'translated' the examples inwhile loops, to help understanding.
– Maxime Recuerda
2 days ago
add a comment |Â
up vote
9
down vote
up vote
9
down vote
In order to make the example more understandable, I will convert both for loops into C# while loops.
VB.NET
string stringValue = "42";
int min = 1;
int max = 10 - stringValue.Length;
int i = min;
while (i <= max)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
C#
string stringValue = "42";
int i = 1;
while (i <= 10 - stringValue.Length)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
The difference is then:
VB.NET caches the maximum value for
i, but C# recomputes it every time.
edited 20 hours ago
camerondm9
485715
answered 2 days ago
Maxime Recuerda
26213
In order to make the example more understandable, I will convert both for loops into C# while loops.
VB.NET
string stringValue = "42";
int min = 1;
int max = 10 - stringValue.Length;
int i = min;
while (i <= max)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
C#
string stringValue = "42";
int i = 1;
while (i <= 10 - stringValue.Length)
stringValue = stringValue + " " + stringValue.Length.ToString();
Console.WriteLine(stringValue);
i++;
The difference is then:
VB.NET caches the maximum value for
i, but C# recomputes it every time.
edited 20 hours ago
camerondm9
485715
answered 2 days ago
Maxime Recuerda
26213
edited 20 hours ago
camerondm9
485715
edited 20 hours ago
camerondm9
485715
edited 20 hours ago
camerondm9
485715
485715
answered 2 days ago
Maxime Recuerda
26213
answered 2 days ago
Maxime Recuerda
26213
answered 2 days ago
Maxime Recuerda
26213
26213
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
It helped me to understand thefor loopsat my begins, I think they are much more understandable. This is why I 'translated' the examples inwhile loops, to help understanding.
– Maxime Recuerda
2 days ago
add a comment |Â
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
It helped me to understand thefor loopsat my begins, I think they are much more understandable. This is why I 'translated' the examples inwhile loops, to help understanding.
– Maxime Recuerda
2 days ago
2
2
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
You don't need to convert loops to while
– Panagiotis Kanavos
2 days ago
10
10
It helped me to understand the
for loops at my begins, I think they are much more understandable. This is why I 'translated' the examples in while loops, to help understanding.– Maxime Recuerda
2 days ago
It helped me to understand the
for loops at my begins, I think they are much more understandable. This is why I 'translated' the examples in while loops, to help understanding.– Maxime Recuerda
2 days ago
add a comment |Â
up vote
5
down vote
Because the for in VB is a different semantic than the for in C# (or any other C-like language)
In VB, the for statement is specifically incrementing a counter from one value to another.
In C, C++, C#, etc., the for statement simply evaluates three expressions:
- The first expression is customarily an initialization
- The second expression is evaluated at the start of each iteration to determine whether the terminal condition has been met
- The third expression is evaluated at the end of each iteration, which is customarily an incrementer.
In VB, you must supply a numeric variable which can be tested against a terminal value and incremented on each iteration
In C, C++, C#, etc., the three expressions are minimally constrained; the conditional expression must evaluate to a true/false (or integer zero/non-zero in C, C++). You don't need to perform an initialization at all, you can iterate any type over any range of values, iterate a pointer or reference over a complex structure, or not iterate anything at all.
So, in C#, etc., the condition expression must be fully evaluated on each iteration, but in VB, the terminal value of the iterator must be evaluated at the beginning, and need not be evaluated again.
answered 2 days ago
C Robinson
1037
add a comment |Â
up vote
5
down vote
Because the for in VB is a different semantic than the for in C# (or any other C-like language)
In VB, the for statement is specifically incrementing a counter from one value to another.
In C, C++, C#, etc., the for statement simply evaluates three expressions:
- The first expression is customarily an initialization
- The second expression is evaluated at the start of each iteration to determine whether the terminal condition has been met
- The third expression is evaluated at the end of each iteration, which is customarily an incrementer.
In VB, you must supply a numeric variable which can be tested against a terminal value and incremented on each iteration
In C, C++, C#, etc., the three expressions are minimally constrained; the conditional expression must evaluate to a true/false (or integer zero/non-zero in C, C++). You don't need to perform an initialization at all, you can iterate any type over any range of values, iterate a pointer or reference over a complex structure, or not iterate anything at all.
So, in C#, etc., the condition expression must be fully evaluated on each iteration, but in VB, the terminal value of the iterator must be evaluated at the beginning, and need not be evaluated again.
answered 2 days ago
C Robinson
1037
add a comment |Â
up vote
5
down vote
up vote
5
down vote
Because the for in VB is a different semantic than the for in C# (or any other C-like language)
In VB, the for statement is specifically incrementing a counter from one value to another.
In C, C++, C#, etc., the for statement simply evaluates three expressions:
- The first expression is customarily an initialization
- The second expression is evaluated at the start of each iteration to determine whether the terminal condition has been met
- The third expression is evaluated at the end of each iteration, which is customarily an incrementer.
In VB, you must supply a numeric variable which can be tested against a terminal value and incremented on each iteration
In C, C++, C#, etc., the three expressions are minimally constrained; the conditional expression must evaluate to a true/false (or integer zero/non-zero in C, C++). You don't need to perform an initialization at all, you can iterate any type over any range of values, iterate a pointer or reference over a complex structure, or not iterate anything at all.
So, in C#, etc., the condition expression must be fully evaluated on each iteration, but in VB, the terminal value of the iterator must be evaluated at the beginning, and need not be evaluated again.
answered 2 days ago
C Robinson
1037
Because the for in VB is a different semantic than the for in C# (or any other C-like language)
In VB, the for statement is specifically incrementing a counter from one value to another.
In C, C++, C#, etc., the for statement simply evaluates three expressions:
- The first expression is customarily an initialization
- The second expression is evaluated at the start of each iteration to determine whether the terminal condition has been met
- The third expression is evaluated at the end of each iteration, which is customarily an incrementer.
In VB, you must supply a numeric variable which can be tested against a terminal value and incremented on each iteration
In C, C++, C#, etc., the three expressions are minimally constrained; the conditional expression must evaluate to a true/false (or integer zero/non-zero in C, C++). You don't need to perform an initialization at all, you can iterate any type over any range of values, iterate a pointer or reference over a complex structure, or not iterate anything at all.
So, in C#, etc., the condition expression must be fully evaluated on each iteration, but in VB, the terminal value of the iterator must be evaluated at the beginning, and need not be evaluated again.
answered 2 days ago
C Robinson
1037
edited 13 hours ago
answered 2 days ago
C Robinson
1037
answered 2 days ago
C Robinson
1037
answered 2 days ago
C Robinson
1037
1037
add a comment |Â
add a comment |Â
up vote
-3
down vote
I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to.
In VB, type the declaration is optional depending on the existence of the Option Explicit setting in the file.
answered yesterday
Terry Carmen
2,0571717
The integer variable they’re referring to isstringValueLength.
– Ry-♦
yesterday
add a comment |Â
up vote
-3
down vote
I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to.
In VB, type the declaration is optional depending on the existence of the Option Explicit setting in the file.
answered yesterday
Terry Carmen
2,0571717
The integer variable they’re referring to isstringValueLength.
– Ry-♦
yesterday
add a comment |Â
up vote
-3
down vote
up vote
-3
down vote
I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to.
In VB, type the declaration is optional depending on the existence of the Option Explicit setting in the file.
answered yesterday
Terry Carmen
2,0571717
I'm more interested in knowing as to why I've had to declare the integer variable and in VB I didn't have to.
In VB, type the declaration is optional depending on the existence of the Option Explicit setting in the file.
answered yesterday
Terry Carmen
2,0571717
edited yesterday
answered yesterday
Terry Carmen
2,0571717
answered yesterday
Terry Carmen
2,0571717
answered yesterday
Terry Carmen
2,0571717
2,0571717
The integer variable they’re referring to isstringValueLength.
– Ry-♦
yesterday
add a comment |Â
The integer variable they’re referring to isstringValueLength.
– Ry-♦
yesterday
The integer variable they’re referring to is
stringValueLength.– Ry-♦
yesterday
The integer variable they’re referring to is
stringValueLength.– Ry-♦
yesterday
add a comment |Â
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5
Microsoft clearly outlines what your problem is...
– Çöđěxěŕ
2 days ago
37
@Çöđěxěŕ: Stop, please. If robotically removing tags from the title without regard to context were helpful, the website would do it.
– Ry-♦
2 days ago
9
@Çöđěxěŕ You can find some info about that here
– pushkin
2 days ago
32
@Çöđěxěŕ I don't think that the two posts contradict each other. The point is: don't awkwardly stick a tag in the title like "question about this thing - tag". But if the title is a complete sentence that includes the tag, then it is sometimes ok. "Why does for loop behave differently when migrating" feels like a way too generic title.
– pushkin
2 days ago
23
@Çöđěxěŕ "migrating VB.NET code to C#" is clearly a full phrase that adds useful information to the title. Don't make edits that decrease clarity. Hopefully, that notion is common sense enough that we don't need a Meta post to back it up.
– jpmc26
2 days ago