View Compilation Error

0_0_18017726_22978.cpp: In function 'char* judge_dec(char*)':
0_0_18017726_22978.cpp:23:17: error: 'strlen' was not declared in this scope
     len=strlen(e);
                 ^
0_0_18017726_22978.cpp: In function 'int main()':
0_0_18017726_22978.cpp:111:52: error: 'strcmp' was not declared in this scope
             if( strcmp( judge_dec(a), judge_dec(b) )==0 )  
                                                    ^
0_0_18017726_22978.cpp:118:38: error: 'strlen' was not declared in this scope
             if( strlen( judge_dec(a) )==0 && strlen( judge_dec(b) )==0 )
                                      ^