View Compilation Error

0_0_16813721_21470.cpp: In function 'int main()':
0_0_16813721_21470.cpp:12:31: error: 'memset' was not declared in this scope
         memset(b, 0, sizeof(b));
                               ^
0_0_16813721_21470.cpp:16:34: error: 'strlen' was not declared in this scope
         for (i = 0; i < strlen(s1); i++)
                                  ^
0_0_16813721_21470.cpp:20:33: error: 'strlen' was not declared in this scope
         for (i = 0; i <strlen(s2); i++)
                                 ^