Ok this wont be that difficult.In the main you got to take the input from the user(what he wants to do) and than use switch(choice) or else you can use nested if else statements.Depending on the choice the user makes each choice would invoke the required function from main.For example
----------------------------------------------------------
int i;
switc(i)
{
case 1: assuming case 1 is addition
int sum = add (x,y)
.
.
}
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So go about this way and you obviously will have to define each function aditon ,subtraction,multiplication and so on.
I suggest you write something and post it coz no one's going to code for you.Let me know if it helped