View Compilation Error

0_0_37174047_20757.cpp: In function 'int main()':
0_0_37174047_20757.cpp:19:37: error: 'memset' was not declared in this scope
         memset(flag, 0, sizeof(flag));
                                     ^
0_0_37174047_20757.cpp:69:44: error: 'strcpy' was not declared in this scope
                     strcpy(num[pr], num[pf]);
                                            ^
0_0_37174047_20757.cpp:70:41: error: 'strlen' was not declared in this scope
                     len = strlen(num[pr]);
                                         ^
0_0_37174047_20757.cpp:84:44: error: 'strcpy' was not declared in this scope
                     strcpy(num[pr], num[pf]);
                                            ^
0_0_37174047_20757.cpp:85:41: error: 'strlen' was not declared in this scope
                     len = strlen(num[pr]);
                                         ^