View Compilation Error

0_0_28023909_17407.c: In function 'is':
0_0_28023909_17407.c:11:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for(int i=2;i<=n;i++){
     ^
0_0_28023909_17407.c:11:5: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_28023909_17407.c:21:21: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
                     for(int k=1;k<=n;k++){
                     ^
0_0_28023909_17407.c:29:17: error: expected expression before '/' token
                 //count--;
                 ^
0_0_28023909_17407.c: In function 'main':
0_0_28023909_17407.c:42:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for(int* i=prime_+1;*i!=41;i++){
     ^
0_0_28023909_17407.c:44:9: error: expected expression before '/' token
         //printf("%d:%d\n",*i, prime[*i]);
         ^
0_0_28023909_17407.c:50:9: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
         for(int i=0;i<21;i++){
         ^