Declaration in for statement in c

Question

Possible Duplicate:
C: for loop int initial declaration

Can we declare some variables in for statement in C programming?If so,in which version of c standard will we find the feature?

@icepack I searched in this site before posting my question,but have not found the duplicate question,why? — prehistoricpenguin, Dec 21 '12 at 13:47
@prehistoricpenguin you can raise this question at http://meta.stackoverflow.com — SomeWittyUsername, Dec 21 '12 at 13:49

score 3 · Answer 1 · answered Dec 21 '12 at 13:47

Yes, you can do that starting with the c99 standard. A straight compile of the code:

int main()
{
   for(int i = 0; i<10; i++)
     printf("%d\n", i);
   return 0;
}

with (the default "gnu89") gcc would give you the answer:

In function main :
error: 'for' loop initial declarations are only allowed in C99 mode
note: use option -std=c99 or -std=gnu99 to compile your code

score 1 · Accepted Answer · answered Dec 21 '12 at 13:50

In C89/C90, all declarations have to appear at the beginning of a block:

/* valid in C89/C90 */
printf("Hello\n");
{
    int i;
    for (i = 0; i < 10; i++) {
        int j = i % 3;
        printf("%d\n", j);
    }
}

Starting with C99 you can mix declarations and statements, and declare variables in the first part of a for:

/* valid in C99 */
printf("Hello\n");
int whatever;
for (int i = 0; i < 10; i++) {
    int j = i % 3;
    printf("%d\n", j);
}

score -1 · Answer 3 · answered Dec 21 '12 at 13:45

-1

In pure C you can't declare variables in for statement. This feature available only in C++. In C all the variables must be declared at the beginning of the code block

answered Dec 21 '12 at 13:45

DuXeN0N

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@prehistoricpenguin that would depend on his definition of what "pure" C is. The C99 spec has not been out very long when you measure against how long the C language has existed, and new features might not be considered to be pure. Indeed, based on Mike's answer, C99 isn't even the default in GCC yet. – mah Dec 21 '12 at 13:54
2

@mah Based on Mike's answer, C89 isn't even the default in GCC yet. Color me unimpressed. – melpomene Dec 21 '12 at 13:57

Declaration in for statement in c

3 Answers3