- Project 6 -
Looping Back and Forth

In this lesson, you learned about Visual C++'s looping capabilities. You saw the following:

• Loops repeat sections of code.
  
  
• The while loop tests a condition at the top of the loop and loops as long as the condition is true.
  
  
• Loops and the if statement differ because the body of an if executes one time at most.
  
  
• The do-while loop tests its condition at the bottom of the loop, ensuring that the loop always executes at least once.
  
  
• The break statement terminates the current loop.
  
  
• The for loop gives you more control when you know in advance the number of iterations required by the loop.
  
  
• When you nest loops, the inner loop iterates faster than the outer loop.
  
  

Project 6 Listing. Using a for loop to compute interest controlled by the user's input.

  1:// Filename: PROJECT6.CPP

  2:// Computes interest over a number of periods

  3:#include <iostream.h>

  4:

  5:

  6:void main()

  7:{

  8:  int periods;       // Number of periods in the loan

  9:  int count;         // Loop control variable

 10:  float intRate;     // Interest rate per period

 11:  float principal;   // Loan amount

 12:

 13:  cout << "Welcome to loan central!" << endl;   // Title

 14:  cout << "------------------------" << endl << endl;

 15:

 16:  cout << "How much was the loan for? ";

 17:  cin >> principal;

 18:

 19:  cout << endl << "What is the interest rate (i.e., .03 ";

 20:  cout << "for 3%) per period? ";

 21:  cin >> intRate;

 22:

 23:  cout << endl << "How many periods are in the loan? ";

 24:  cin >> periods;

 25:

 26:  for (count = 0; count < periods; count++)

 27:    { principal *= (1 + intRate); }   // Compounds the interest

 28:

 29:  cout.precision(2);

 30:  cout.setf(ios::showpoint);

 31:  cout.setf(ios::fixed);

 32:  cout << endl << "$" << principal << " total amount owed after "

 33:       << periods << " periods." << endl;

 34:  return;

 35:}

Output

Welcome to loan central!

------------------------

How much was the loan for? 2500.00

What is the interest rate (i.e., .03 for 3%) per period? .11

How many periods are in the loan? 5

$4212.65 total amount owed after 5 periods.

Description

1: A C++ comment that includes the program's filename.

2: A C++ comment that contains the program's description.

3: cout and cin need information in the IOSTREAM.H header file.

4: Place blank lines throughout a program for readability.

5: Place blank lines throughout a program for readability.

6: All functions have names, and the first function in all C++ programs is main().

7: All functions begin with a left brace.

8: Defines an integer variable that will hold the number of periods in the loan.

9: Defines an integer variable that will control the for loop.

10: Defines a floating-point variable that will hold the interest rate.

11: Defines a floating-point variable that will hold the loan principal (the amount borrowed).

12: Extra blank lines make your program more readable.

13: Prints a title.

14: Underlines the title on-screen with hyphens.

15: Extra blank lines make your program more readable.

16: Prompts the user for the amount of the loan (the principal).

17: Gets the principal from the user.

18: Extra blank lines make your program more readable.

19: Prompts for the interest rate. The user is reminded to enter the interest as a decimal.

20: The rest of line 19's cout.

21: Gets the interest rate.

22: Extra blank lines make your program more readable.

23: Prompts for the number of periods in the loan (called the loan term).

24: Gets the term from the user.

25: Extra blank lines make your program more readable.

26: The for loop ensures that the interest calculation computes for the full term entered by the user in line 25.

27: The body of the for loop is only a single statement. The principal increases by the amount of each period's interest rate.

28: Extra blank lines make your program more readable.

29: Ensures that two decimal places print.

30: Prints the decimal point.

31: Guards against scientific notation.

32: Prints the computed loan principal including all accrued interest.

33: Continues the loan balance's printing.

34: Returns to QuickWin control window.

38: main()'s closing brace to terminate the program.

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1: You saw another version of this program in Unit 7, but that program didn't have the looping capability that this program does. As a result, Unit 7's program was longer and less flexible!

9: All for loops require a loop control variable.

26: The for loop compounds the loan in one step.

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