Date assigned: 2/4/03
Suppose that you need to make a given amount of change, and you would like to use the fewest coins to do it. The available coins are quarters, dimes, nickles and pennies. How can you make the change?
One approach is to start by taking as many quarters as you can without getting too much. For example, to make 64 cents, you take two quarters, since three quarters would be too much. Notice that, if you divide 64 by 25, you get a quotient of 2, with a remainder of 14.
Next, take as many dimes as you can without getting too much. If there is 14 cents left, you need to take 1 dime. Notice that, if you divide 14 by 10, you get a quotient of 1 and a remainder of 4.
Do a similar thing with nickles and pennies. Of course, there is no need to divide by 1. Once you reach the pennies, everything left over is pennies.
This is an exercise in the use of functions. Write each of the following as a separate function. Write a clear and concise contract for each function. The solution that you turn in must have a clear contract for each function. Solutions without contracts will not be acceptable.
Write a function with a void result type that has two reference parameters and two value parameters.
The value parameters are information coming into the function. They tell the function two things: (1) an amount of change that needs to be made, and (2) the worth of a particular coin. For example, this function might be told to make 82 cents, and that the value of the coin is 25.
The two reference parameters are values coming out of the function. They should tell the caller how many of that coin to use, and how much is left over. For example, if the desired amount of change is 82 cents and the coin value is 25 cents, then the function should say to use 3 coins, with 7 cents left over. (Three quarters plus 7 more cents gives 82 cents.)
Write a function that has a void result type, one value parameter and four reference parameters.
The value parameter tells information coming into the function, and it is an amount of change that needs to be made.
The four reference parameters are information coming out of the function. They should be set to the number of quarters, dimes, nickles and pennies (one number per parameter) that should be used to make the requested amount of change. This function should use the preceding one.
Write a function that has no parameters, and has a result type of int. This function should prompt the user for an amount of change, read the amount, and return the amount as its value.
Write a main function that repeatedly reads an amount of change from the user and prints the number of quarters, dimes, nickles and pennies to use for that amount of change. Make your program's output clear and readable, not just raw numbers. The program should continue asking until a negative number is typed in by the user. At that point, the program should stop, without saying how many coins to use to make the negative amount of change.
The main function must use the functions described above to do the work. It should not do everything itself. It should be short and simple.
To develop this program, use successive refinement. Do not write the entire program and then test it. Instead, write ONE function. Write a short main program to test that function. Make sure that function is working before going on to the next function.
Successive refinement is a tool that is an absolute necessity for writing software. It allows you to isolate mistakes. If each function that you create is tested when it is written, then any mistake is most likely in the most recently written function. This makes mistakes much easier to find and fix than if the mistake could be anywhere in a program. If you write an entire program and try to test it, not only can a mistake be anywhere, but there will surely be several mistakes, and they will often act together to make it confusing about where the mistakes are located.
Use successive refinement for this program, even if you do not think that you need it. You will need it later, and will want experience using it.