View Compilation Error

0_0_15864989_6146.c: In function 'KthNumber':
0_0_15864989_6146.c:23:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for (int j = 0; j < k; ++j)
  ^
0_0_15864989_6146.c:23:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
0_0_15864989_6146.c:26:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for (int i = size; i > half; --i)
   ^
0_0_15864989_6146.c: In function 'main':
0_0_15864989_6146.c:51:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for (int i = 1; i <= n; ++i)
   ^
0_0_15864989_6146.c:52:17: error: 'num' undeclared (first use in this function)
    scanf("%d", &num[i]);
                 ^
0_0_15864989_6146.c:52:17: note: each undeclared identifier is reported only once for each function it appears in