View Compilation Error

0_0_15632124_11367.cpp: In function 'int main()':
0_0_15632124_11367.cpp:15:17: error: 'strlen' was not declared in this scope
   len=strlen(str);
                 ^
0_0_15632124_11367.cpp:23:38: error: 'strcmp' was not declared in this scope
        if(!strcmp(word[k],word[count]))
                                      ^
0_0_15632124_11367.cpp:25:48: error: 'memset' was not declared in this scope
         memset(word[count],0,sizeof word[count]);
                                                ^