foo.c: In function 'fib67':
foo.c:6:5: error: 'for' loop initial declarations are only allowed in C99 mode
     for(int i=0;i<n-1;i++)
     ^
foo.c:6:5: note: use option -std=c99 or -std=gnu99 to compile your code
foo.c: In function 'main':
foo.c:20:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^