View Compilation Error

0_0_18664221_31824.cpp: In function 'int main()':
0_0_18664221_31824.cpp:21:24: error: 'strlen' was not declared in this scope
   while (i < strlen(buf)) {
                        ^
0_0_18664221_31824.cpp:27:32: error: 'memset' was not declared in this scope
    memset(word, 0, sizeof(word));
                                ^