View Compilation Error

0_0_17589703_32544.cpp: In function 'int main()':
0_0_17589703_32544.cpp:20:25: error: 'strlen' was not declared in this scope
   int len1 = strlen(str1), len2 = strlen(str2);
                         ^
0_0_17589703_32544.cpp:24:23: error: 'len2' was not declared in this scope
   for (int i = 0; i < len2; i++)
                       ^