CIS3355: Business Data Structures
Fall, 2008
 

Functions

The intent of this program is to learn about how functions work. We are going to take your previous program and clean it up using functions. There is only one part to this assignment.

I am going to give you my main function, and all of the include and function prototypes I used:

#include <iostream.h>

void displaymenu();
void checkchoice(char choice);
int getaninteger(short number)
float getafloat(short number);
void addintegers(int int1, int int2);
void subtractintegers(int int1, int2);
void multiplyintegers(int int1, int int2);
void divideintegers(int int1, int int2);
void getquotient(int int1, int int2)
void getremainder(int int1, int int2);
void multiply(float float1, float2);
void divide(float float1, float float2);

void main()
{
    char menuchoice;
    int intvalue1; intvalue2;
    float fvalue1, fvalue2

// Present the Main menu
    displaymenu();

// get the user selection
    cin >> menuchoice;

// Check the user selection
    checkchoice(menuchoice);

// Get user entered integers
    if ((menuchoice >= '1) && (menuchoice <= '6'))
    {
        intvalue1 = getaninteger(1);
        intvalue2 = getaninteger(2);
    }

// Get user entered reals
    if ((menuchoice == '7') || (menuchoice = 8));
    {
        fvalue1 = getafloat(1);
        fvalue2 = getafloat(2);
    }

// Perform the operation requested
    switch (menuchoice)
    {
        case '1' : addintegers(intvalue1, intvalue2); break;
        case '2' : subtractintegers(intvalue1, intvalue2); break;
        case '3' : multiplyintegers(intvalue1, intvalue2); break;
        case '4' : divideintegers(intvalue1, intvalue2); break;
        case '5' : getquotient(intvalue1, intvalue2);
        case '6' : getremainder(intvalue1, intvalue2); break;
        case '7' : multiply(fvalue1, fvalue2); break;
        case '8' : divide(fvalue1, fvalue2); break;
    }
}

Are there errors? A few, but they are easily corrected.

Let's take a look at a few of the functions.

void displaymenu()

Remember the basics of functions:

1. They must have a unique name (in this case displaymenu)
2. They May require arguments or parameters (or may not, as in this case)
3. They may return a value (or may not, as in this case)

What does this function do? It presents the menu to the user. It is almost trivial. In fact, I will even give it to you:

void displaymenu()
{
    cout << "Enter your choice:\n\n";
    cout << " 1. Add two integers\n";
    cout << " 2. Subtract an integer from another integer\n";
    cout << " 3. Multiply two integers\n";
    cout << " 4. Divide two integers\n";
    cout << " 5. Find the Quotient of two integers\n";
    cout << " 6. Find the Remainder of two integers\n";
    cout << " 7. Multiply two Real Numbers\n";
    cout << " 8. Divide two Real Numbers\n";
    cout << "? ";
}

The only other thing you should keep in mind is that all functions come after the main function. Make sure you add the function after the end of the main function.

    int getaninteger(short number)

Again, this function:

1. Has a unique name (in this case getaninteger)
2. Passes an argument or parameter (in this case, a short integer)
3. Returns an integer value

How does it work? Let's look at how it is used in the code:

    if ((menuchoice >= '1) && (menuchoice <= '6'))
    {
        intvalue1 = getaninteger(1);
        intvalue2 = getaninteger(2);
    }

As you will remember, if the user chose any of the menu choices '1' through '6', that meant they wanted to perform an operation using an integer. That meant that the first thing we had to do was get the two integers they wanted to work with.

What are we passing the function? In this case the number of the integer (either 1 or 2). This might make more sense if we look at the output:

The first time we call the function (intvalue1 = getaninteger(1);), we pass it the value 1. Hence the output:

Enter integer number 1:

The second time we call the function (intvalue2 = getaninteger(2);), we pass it the value 2. Hence the output:

Enter integer number 2:

What does it return? An integer value. That is what we said it would return when we declared it as:

    int getaninteger(short number)

What does it do with it? The first time it is called it places the integer in location intvalue1 (intvalue1 = getaninteger(1);); the second time it is called, it places it in intvalue2 (intvalue2 = getaninteger(2);)

Once again, I'll even give you the code for the function:

int getaninteger(short number)
{
    int aninteger;

    cout << "\nEnter integer number " << number <<": ";
    cin >> aninteger;
    cout << "\nThe integer entered was: " << aninteger << endl;

    return(aninteger);
}

Pretty straight-forward. As for the other functions, well, I think you can figure them out on your own. For the most part, it is simply a situation of taking them out of the main function, and setting them up as functions of their own. We can, however, look at some of the parameters passed and values returned for each of the functions:

This page was last updated on 07/06/05