View Compilation Error

0_0_17954055_19691.c: In function 'sushu':
0_0_17954055_19691.c:4:5: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
     for(int i=2;i*i<=a;i++)
     ^
0_0_17954055_19691.c:4:5: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code