View Compilation Error

0_0_23080866_1403.cpp: In function 'void re(char*)':
0_0_23080866_1403.cpp:4:23: error: 'strlen' was not declared in this scope
     int len = strlen(s);  
                       ^
0_0_23080866_1403.cpp: In function 'int main()':
0_0_23080866_1403.cpp:30:28: error: 'scanf' was not declared in this scope
     while(~scanf("%s%s",a,b))  
                            ^
0_0_23080866_1403.cpp:36:22: error: 'strcmp' was not declared in this scope
         if(strcmp(a,b))  
                      ^
0_0_23080866_1403.cpp:37:26: error: 'printf' was not declared in this scope
             printf("NO\n");  
                          ^
0_0_23080866_1403.cpp:39:27: error: 'printf' was not declared in this scope
             printf("YES\n");  
                           ^