View Compilation Error

0_0_24012482_19813.c: In function 'main':
0_0_24012482_19813.c:33:2: error: expected expression before '/' token
  //pre_cal();
  ^
0_0_24012482_19813.c:40:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for(int i=1;i<=5;i++)
   ^
0_0_24012482_19813.c:40:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code