The do while Statement

Why the do while Stmt

The for loop is used when you know exactly how many iterations there should be.

The while loop is used when there are an indeterminant number of iterations.  The number of iterations vary from zero and upward.

There are times that you want the loop body to be executed at least once.  That is, the condition need not be tested until after the loop body is executed one time through.

while(condition){

   loop body

}

do {

   loop body

} while(condition);

Uses of the do while

Typical use of the do while:

• Entering a prompt and checking for validity and continue to prompt until valid data is entered.

char nextOption()

{ // post: Return an uppercase W, D, or Q

  char option = '?';

  do {

    cout<<"W)ithdraw, D)eposit,or Q)uit: ";

    cin >> option;

    option = toupper(option);

  } while((option != 'W') &&

          (option != 'D') &&

          (option != 'Q'));

  return option;

}

int main()

{

  char choice = 'Q';



  do {

    choice = nextOption();

    // assert: choice is either 'Q', 'W', or 'D'

    if('W' == choice)

      cout << "\nValid entry--process W\n" << endl;

    if('D' == choice)

      cout << "\nValid entry--process D\n" << endl;

    if('Q' == choice)

      cout << "\nHave a nice whatever :)" << endl;

  } while ( choice != 'Q' );



  return 0;

}

The Temperature Averages Revisited

// Determine the range of temperatures in a set of known size

#include <iostream>

using namespace std;



int main()

{

  int aTemp;

  int highest = -9999; // No temperature will be less than -9999

  int lowest = 9999;   // No temperature will be greater than 9999

  int j, n, range;



  cout << "Enter number of temperature readings: ";

  cin >> n;

         // Input first temperature to record it as highest and lowest

  cout << "Enter readings 1 per line" << endl;

  for(j = 1; j <= n; j++)

  cin >> aTemp;

  do {

               // Update the highest so far, if necessary

    if(aTemp > highest)

      highest = aTemp;

               // Update the lowest so far, if necessary

    if(aTemp < lowest)

      lowest = aTemp;

               // Get the next input

  } while(cin >> aTemp);



  range = highest - lowest;

  cout << "Range: " << range << endl;



  return 0;

} 

The Guessing Game

Page 329. Project 8F.

Generate a random number between 1 and 100.

Enter a guess.

While the guess is not the random number

if the guess is less than the number then print "too low" else "too high"

enter the next guess