View Compilation Error

0_0_25402242_31870.c:10:1: error: unknown type name 'bool'
 bool ok(int x,int y)
 ^
0_0_25402242_31870.c: In function 'ok':
0_0_25402242_31870.c:13:10: error: 'false' undeclared (first use in this function)
   return false;
          ^
0_0_25402242_31870.c:13:10: note: each undeclared identifier is reported only once for each function it appears in
0_0_25402242_31870.c:14:9: error: 'true' undeclared (first use in this function)
  return true;
         ^
0_0_25402242_31870.c: In function 'dfs':
0_0_25402242_31870.c:30:2: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
  for(int i=1;i<5;i++)
  ^
0_0_25402242_31870.c:30:2: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code