View Compilation Error

0_0_33187094_16907.cpp: In function 'int main()':
0_0_33187094_16907.cpp:54:36: error: 'strlen' was not declared in this scope
         int cnt = 0, len = strlen(s), ans = 0;
                                    ^
0_0_33187094_16907.cpp:73:21: error: 'ans' was not declared in this scope
                     ans += (1 << k);
                     ^
0_0_33187094_16907.cpp:78:17: error: 'ans' was not declared in this scope
                 ans += (1 << i);
                 ^
0_0_33187094_16907.cpp:83:23: error: 'ans' was not declared in this scope
         if((len + 1 - ans) & 1) ans++;
                       ^
0_0_33187094_16907.cpp:84:23: error: 'ans' was not declared in this scope
         printf("%d\n",ans);
                       ^