Question

I’m looking at this page which says:

In C++ you can declare variables pretty much anywhere in your program. This is not the case with C. Variables must be declared at the beginning of a function and must be declared before any other code. This includes loop counter variables, which means you can’t do this:

for(int i = 0; i < 200; i++) {

Forgetting that you can’t declare variables just anywhere is one of
the most frequent causes of ‘it won’t compile’ problems for
programmers moving from C++ to C.

I’ve been using Objective-C for a while, and thus C, and I have no problems with a statement such as for(int i = 0; i < 200; i++) { and yet Objective-C is C, strictly, so what is this web page referring to?

Answer 1

The web page is inaccurately characterizing C89.

In C89, you could declare variables at the top of any block (not just at the start of a function), but not at any point during a block.

In C99 and beyond, you are not constrained to declare variables at the beginning of a block. Specifically, C99 allows you to write:

for (int i = 0; i < max; i++)

If you use GCC but need to retain compatibility with MSVC, then you can use -Wdeclaration-after-statement to detect when you declare a variable after a statement (which C89 does not allow).

Objective C presumably uses C99 rather than C89 as the standard it extends, so it allows variable declarations when needed.