View Compilation Error

1_733_2705_23022.cpp: In function 'int main()':
1_733_2705_23022.cpp:12:35: error: 'strlen' was not declared in this scope
            for(int i=0;i<=strlen(s);i++)
                                   ^
1_733_2705_23022.cpp:22:15: error: 'sum' was not declared in this scope
 printf("%d\n",sum);
               ^