View Compilation Error

0_0_13927479_28742.cpp: In function 'int main()':
0_0_13927479_28742.cpp:52:33: error: 'strlen' was not declared in this scope
                 if(strlen(str[i]) > len) {  
                                 ^
0_0_13927479_28742.cpp:59:48: error: 'strlen' was not declared in this scope
                 end = end * len + strlen(str[i]);  
                                                ^