Homework 8, An Introduction to Functions.

Short Description:

Modify a solution to homework 2 to include functions.

This assignment is worth 10 points.

Goals

When you finish this homework, you should have:

Started learning about functions.

Formal Description

In this homework we will begin to learn about functions. There are a number of basic concepts you will be learning

Declaring function prototypes
- Basic parameters.
- Function return values.
Defining functions.
Calling functions.

We will discuss all of these pieces in class, so this exercise is designed to provide a simple introduction and make you familiar with the practice of functions.

More details can be found in chapter 8 of your book.

Get the starting source code file.

Begin by downloading this file
- In most browsers you can right click on the file and select save link as.
This is my solution to the second program.

It has way too much repeated code.

Notice the input is done twice

// get the starting position
cout << "Enter the starting cubits => ";
cin >> inputCubits;
cout << "Enter the starting palms => ";
cin >> inputPalms;
cout << "Enter the starting fingers => ";
cin >> inputFingers;

The conversion to fingers is done multiple times

startFingers = inputFingers + inputPalms * FINGERS_PER_PALM +
                   inputCubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

The conversion from fingers to fingers, palms and cubits is repeated three times.

fingers = startFingers % FINGERS_PER_PALM;
startFingers /= FINGERS_PER_PALM;
palms = startFingers % PALMS_PER_CUBIT;
cubits = startFingers / PALMS_PER_CUBIT;

Finally, the output is performed multiple times

cout << "             ended   at: " << cubits << " cubits "
     << palms << " palms " << fingers << " fingers " << endl;

When you see a section of code repeated multiple times, this is a good candidate for a function.

Put your name and class information at the top of this program.

Write a function to compute fingers from the values of fingers, palms, and cubits.

startFingers = inputFingers + inputPalms * FINGERS_PER_PALM +
                   inputCubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

Think of this as a mathematical expression (which it is)
- It takes three input values (the distance in fingers, palms, and cubits)
- It returns a single value, the total distance in fingers.
Thus a function to do this will take three parameters and return a single value.
To write this function we need to do three things.
1. Create a function prototype
2. Create a function definition
3. Call the function.

Create the function prototype
- At the top of the program after the constants but be fore main insert the following
- ```
int ConvertToFingers(int fingers, int palms, int cubits); 
```
- Your code should look like this:
```
const int GRAINS_PER_FINGER{1};

int ConvertToFingers(int fingers, int palms, int cubits);

int main() { 
```
- This function will take three integer parameters fingers, palms and cubits.
- And will return a single integer value.

Create a function definition

This is below the end of main.

int ConvertToFingers(int fingers, int palms, int cubits) {
    int totalFingers{0};

    totalFingers = fingers + palms * FINGERS_PER_PALM +
                   cubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

    return totalFingers;
}

Your final code will look like this

    return 0;
}

int ConvertToFingers(int fingers, int palms, int cubits) {
    int totalFingers{0};

    totalFingers = fingers + palms * FINGERS_PER_PALM +
                   cubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

    return totalFingers;
}

Notice, the parameters are used in the computation.
But totalFingers is a local variable
- The type matches the function return type.
- And it is returned.

Finally use function

Change the line

startFingers = inputFingers + inputPalms * FINGERS_PER_PALM +
             inputCubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

To be

startFingers = ConvertToFingers(inputFingers, inputPalms, inputCubits);

Note that the variable names passed as arguments do not match the parameter names.
- This is acceptable, they must match in position and type.

Change the line

endFingers = inputFingers + inputPalms * FINGERS_PER_PALM +
             inputCubits * PALMS_PER_CUBIT * FINGERS_PER_PALM;

To be

endFingers = ConvertToFingers(inputFingers, inputPalms, inputCubits);

Write a function to do the input.

Create the function prototype
- Functions in c/c++ can only return one thing, so we will need to make reference parameters
- These are parameters that will change the value of the arguments.
- They have a & between the type and the parameter name.
- We will also pass a description for the prompts.
- Since this function does not return a value, it will be a void function.
- At the top of the program, by the other function prototype put
```
void GetInput(int & fingers, int & palms, int & cubits, string pos); 
```

Create the function definition

At the bottom of the file insert the following

void GetInput(int & fingers, int & palms, int & cubits, string pos){

    cout << "Enter the " << pos << " cubits => ";
    cin >> cubits;

    cout << "Enter the " << pos << " palms => ";
    cin >> palms;

    cout << "Enter the " << pos << " fingers => ";
    cin >> fingers;

    return;
}

Call the function.

Replace

cout << "Enter the starting cubits => ";
cin >> inputCubits;
cout << "Enter the starting palms => ";
cin >> inputPalms;
cout << "Enter the starting fingers => ";
cin >> inputFingers;

With

GetInput(inputFingers, inputPalms, inputCubits, "starting");

Replace

cout << "Enter the ending cubits => ";
cin >> inputCubits;
cout << "Enter the ending palms => ";
cin >> inputPalms;
cout << "Enter the ending fingers => ";
cin >> inputFingers;

With

GetInput(inputFingers, inputPalms, inputCubits, "ending");

Write a function to reduce the units.

Create the function prototype
- This function will take one value (the total fingers)
- And will return three values (finger, palms and cubits)
- So the function prototype will be
```
ReduceFingers(int totalFingers, int & fingers, int & palms, int & cubits); 
```
- Add this function prototype at the top.

Create the function definition

Add the following function at the bottom of the file

void ReduceFingers(int totalFingers, int & fingers, int & palms, int & cubits){
    fingers = totalFingers % FINGERS_PER_PALM;
    totalFingers /= FINGERS_PER_PALM;
    palms = totalFingers % PALMS_PER_CUBIT;
    cubits = totalFingers / PALMS_PER_CUBIT;

    return;
}

Call the function.

Replace the three repeated version of the code with a function call.

The first will be replace

fingers = startFingers % FINGERS_PER_PALM;
startFingers /= FINGERS_PER_PALM;
palms = startFingers % PALMS_PER_CUBIT;
cubits = startFingers / PALMS_PER_CUBIT;

With

ReduceFingers(startFingers, fingers, palms, cubits);

Repeat this, make sure you get the first parameter correct.

Write a function to do the output.

Create the function prototype
- This function will take the three units.
- And print them out with labels.
- It should not change anything so these will be value parameters.
- It will not return anything, so the it will be a void function.
```
void PrintUnits(int fingers, int palms, int cubits); 
```

Create the function definition

void PrintUnits(int fingers, int palms, int cubits){
    cout << cubits << " cubits "
         << palms << " palms "
         << fingers << " fingers";

    return;
}

Call the function.

Replace all code that looks like this:

cout << "Nebi and Ako started at: " << cubits << " cubits "
     << palms << " palms " << fingers << " fingers " << endl;

With this

cout << "Nebi and Ako started at: ";
PrintUnits(fingers, palms, cubits);
cout << endl;

If you need a reference, my code is here

Required Files

A single source code file. The starting code with the modifications described in the exercise.

Submission

Submit the assignment to the D2L folder Homework 8 by the due date.