delegate int Operation(int val1, int val2); 
public int Add(int val1, int val2) 
{ 
return val1 + val2; 
} 
public int Subtract (int val1, int val2) 
{ 
return val1- val2; 
} 
public void Perform() 
{ 
Operation Oper; 
Console.WriteLine("Enter + or - "); 
string optor = Console.ReadLine(); 
Console.WriteLine("Enter 2 operands"); 

string opnd1 = Console.ReadLine(); 
string opnd2 = Console.ReadLine(); 

int val1 = Convert.ToInt32 (opnd1); 
int val2 = Convert.ToInt32 (opnd2); 

if (optor == "+") 
Oper = new Operation(Add); 
else 
Oper = new Operation(Subtract); 

Console.WriteLine(" Result = {0}", Oper(val1, val2)); 
}