View Compilation Error

0_0_13570583_21659.c: In function 'is_prime':
0_0_13570583_21659.c:4:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int i=2;i*i<=x;i++){
  ^
0_0_13570583_21659.c:4:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_13570583_21659.c: In function 'is_huiwen':
0_0_13570583_21659.c:16:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int i=0;i<=n/2-1;i++){
  ^
0_0_13570583_21659.c: In function 'main':
0_0_13570583_21659.c:24:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i=a;i<=b&&i<10000000;i++){
   ^