ISO C90 forbids mixed declarations and code in C

I declared a variable in this way:

int i = 0;

I get the warning:

ISO C90 forbids mixed declarations and code

How can I fix it?

I think you should move the variable declaration to top of block. I.e.

{
    foo();
    int i = 0;
    bar();
}

to

{
    int i = 0;
    foo();
    bar();
}

Up until the C99 standard, all declarations had to come before any statements in a block:

void foo()
{
  int i, j;
  double k;
  char *c;

  // code

  if (c)
  {
    int m, n;

    // more code
  }
  // etc.
}

C99 allowed for mixing declarations and statements (like C++). Many compilers still default to C89, and some compilers (such as Microsoft's) don't support C99 at all.

So, you will need to do the following:

1. Determine if your compiler supports C99 or later; if it does, configure it so that it's compiling C99 instead of C89;

2. If your compiler doesn't support C99 or later, you will either need to find a different compiler that does support it, or rewrite your code so that all declarations come before any statements within the block.