View Compilation Error

0_0_13962929_18740.cpp: In function 'int main()':
0_0_13962929_18740.cpp:52:20: error: 'strlen' was not declared in this scope
    if(strlen(str[i]) > len) {
                    ^
0_0_13962929_18740.cpp:59:35: error: 'strlen' was not declared in this scope
    end = end * len + strlen(str[i]);
                                   ^