View Compilation Error

0_0_30943655_6455.cpp: In function 'int main()':
0_0_30943655_6455.cpp:9:17: error: 'strcat' was not declared in this scope
     strcat(a1,a2);
                 ^
0_0_30943655_6455.cpp:10:17: error: 'strlen' was not declared in this scope
     if(strlen(a1)!=strlen(b1)  cout<<"NO\n";
                 ^
0_0_30943655_6455.cpp:10:32: error: expected ')' before 'cout'
     if(strlen(a1)!=strlen(b1)  cout<<"NO\n";
                                ^
0_0_30943655_6455.cpp:21:3: error: expected '}' at end of input
   }
   ^