View Compilation Error

0_0_17022469_20759.cpp: In function 'int main()':
0_0_17022469_20759.cpp:52:17: error: 'strlen' was not declared in this scope
 if(strlen(str[i]) > len) {
                 ^
0_0_17022469_20759.cpp:59:44: error: 'strlen' was not declared in this scope
             end = end * len + strlen(str[i]);
                                            ^
0_0_17022469_20759.cpp:64:1: error: 'return0' was not declared in this scope
 return0;
 ^