Return data type and passing argument in user defined function

#include<iostream>

int sum(int a, int b);

using namespace std;

main()

{

               int x,y,result;

               cout<<"enter two number:";

               cin>>x>>y;

               result=sum (x,y);

               cout<<"sum="<<result;

               return 0;

              

}

int sum(int a,int b)

{

               int c;

               c=a+b;

               return (c);

              

}