View Compilation Error

0_0_25879849_30748.cpp: In function 'll check(int, ll)':
0_0_25879849_30748.cpp:45:20: error: 'strlen' was not declared in this scope
  int len = strlen(c), ans = 0;
                    ^
0_0_25879849_30748.cpp:48:3: error: 'ans' was not declared in this scope
   ans *= 10;
   ^
0_0_25879849_30748.cpp:52:6: error: 'ans' was not declared in this scope
  if (ans == 0)
      ^
0_0_25879849_30748.cpp: In function 'll cnt(int, ll)':
0_0_25879849_30748.cpp:59:24: error: 'memset' was not declared in this scope
  memset(c, 0, sizeof(c));
                        ^
0_0_25879849_30748.cpp:65:20: error: 'strlen' was not declared in this scope
  int len = strlen(c), ans = 0;
                    ^
0_0_25879849_30748.cpp:68:3: error: 'ans' was not declared in this scope
   ans *= 10;
   ^
0_0_25879849_30748.cpp:72:9: error: 'ans' was not declared in this scope
  return ans;
         ^