View Compilation Error

0_0_16120643_30166.cpp: In function 'int main()':
0_0_16120643_30166.cpp:16:25: error: 'strlen' was not declared in this scope
   int len1 = strlen(str1), len2 = strlen(str2);
                         ^
0_0_16120643_30166.cpp:17:27: error: 'memset' was not declared in this scope
   memset(s1, 0, sizeof(s1));
                           ^
0_0_16120643_30166.cpp:23:12: error: 'len2' was not declared in this scope
   for (j = len2 - 1; j >= 0; j--)
            ^