View Compilation Error

0_0_28329078_32296.c: In function 'main':
0_0_28329078_32296.c:8:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i=0;i<strlen(a)/2;i++){
   ^
0_0_28329078_32296.c:8:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_28329078_32296.c:11:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for(int k=1,ff=i+1;k<strlen(b);k++,ff++){
     ^