Where can I legally declare a variable in C99?

Question

When I was first introduced to C I was told to always declare my variables at the top of the function. Now that I have a strong grasp of the language I am focusing my efforts on coding style, particularly limiting the scope of my variables. I have read about the benefits to limiting the scope and I came across an interesting example. Apparently, C99 allows you to do this... ``` for (int i = 0; i < 10; i++) { puts("hello"); } ``` I had thought that a variables scope was limited by the inner-most surrounding curly braces `{ }`, but in the above example `int i` appears to be limited in scope by the curly braces of the for-loop even though it is declared outside of them. I tried to extend the above example with `fgets()` to do what I thought was something similar but both of these gave me a syntax error. `fgets(char fpath[80], 80, stdin);` *See Note** `fgets(char* fpath = malloc(80), 80, stdin);` So, just where exactly is it legal to declare variables in C99? Was the for-loop example an e…

Accepted Answer

In C99, you can declare your variables where you need them, just like C++ allows you to do that.

```
void somefunc(char *arg)
{
    char *ptr = "xyz";
    if (strcmp(arg, ptr) == 0)
    {
        int abc = 0;    /* Always could declare variables at a block start */

somefunc(arg, &ptr, &abc);

int def = another_func(abc, arg);   /* New in C99 */
        ...other code using def, presumably...
    }
}
```

You can declare a variable in the control part of a 'for' loop:

```
  for (int x = 0; x < 10; x++)    /* New in C99 */
```

You cannot declare a variable in the control part of a 'while' loop or an 'if' statement.

You cannot declare a variable in a function call.

Obviously, you can (and always could) declare variables in the block after any loop or an 'if' statement.

The C99 standard says:

6.8.5.3 The for statement

The statement

```
for ( clause-1 ; expression-2 ; expression-3 ) statement
```

behaves as follows: The expression expression-2 is the controlling expression that is evaluated before each execution of the loop body. The expression expression-3 is evaluated as a void expression after each execution of the loop body. If clause-1 is a declaration, the scope of any variables it declares is the remainder of the declaration and the entire loop, including the other two expressions; it is reached in the order of execution before the first evaluation of the controlling expression. If clause-1 is an expression, it is evaluated as a void expression before the first evaluation of the controlling expression.

Where can I legally declare a variable in C99?

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