View Compilation Error

0_0_32885835_21961.cpp: In function 'int main()':
0_0_32885835_21961.cpp:9:30: error: 'strlen' was not declared in this scope
   for(int i = 0; i < strlen(s); i++){
                              ^
0_0_32885835_21961.cpp:10:19: error: 'max' was not declared in this scope
    x = max(s[i], x);
                   ^
0_0_32885835_21961.cpp:12:30: error: 'strlen' was not declared in this scope
   for(int i = 0; i < strlen(s); i++){
                              ^