How to compile a C project in C99 mode?

Question

I got the following error message while compiling the C code:

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

What does it mean?

How to fix it?

Answer 1

You have done this:

for (int i=0;i<10;i++) { 

And you need to change it to this:

int i; for (i=0;i<10;i++) { 

Or, as the error says,

use option -std=c99 or -std=gnu99 to compile your code.

Update copied from Ryan Fox's answer:

gcc -std=c99 foo.c -o foo 

Or, if you're using a standard makefile, add it to the CFLAGS variable.