I'm just going to fix formatting issues here and let you deal with the code as needs be. Compare to your original code so you don't make these same mistakes again.
Code:
#include <iostream>
using namespace std;
int input;
int mult ( int x, int y);
int main()
{
int x;
int y;
// You had an extra declaration of main here. Too much copy and paste, I think.
cout<<"enter two numbers (seperated by a space): ";
cin>> x >> y;
cin.ignore ();
cout<<"the answer is "<< mult ( x, y ) <<"\n";
cin.get();
}
int mult ( int x, int y )
{
int input;
cout<<"1. multiply\n";
cout<<"2. devide\n";
cout<<"3. subtract\n";
cout<<"4. add\n";
cout<<"Selection: ";
cin>>input;
switch ( input ) { // The brackets in every one of your case statements...
case 1: // ... didn't do anything (good or bad) in this case...
return x * y; // ... so I removed them. In switch statements it's the
break; // ... break statement that's important.
case 2:
return x / y;
break;
case 3:
return x - y;
break;
case 4:
return x + y;
break;
default:
cout<<"Error, bad input, quitting\n";
} // of course you do need brackets around the whole case statement.
}
There are still alot of issues with the code, but this should get you to compiling it.