View Compilation Error

0_0_27589657_18536.c: In function 'main':
0_0_27589657_18536.c:11:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(ll i=2;i*i<m;++i){
   ^
0_0_27589657_18536.c:11:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code