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Thinking in C++
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while, do-while, and for control looping. A statement repeats until the controlling expression evaluates to false. The form of a while loop is


The expression is evaluated once at the beginning of the loop and again before each further iteration of the statement.

This example stays in the body of the while loop until you type the secret number or press control-C.

//: C03:Guess.cpp
// Guess a number (demonstrates "while")
#include <iostream>
using namespace std;

int main() {
  int secret = 15;
  int guess = 0;
  // "!=" is the "not-equal" conditional:
  while(guess != secret) { // Compound statement
    cout << "guess the number: ";
    cin >> guess;
  cout << "You guessed it!" << endl;
} ///:~

The while’s conditional expression is not restricted to a simple test as in the example above; it can be as complicated as you like as long as it produces a true or false result. You will even see code where the loop has no body, just a bare semicolon:

while(/* Do a lot here */)

In these cases, the programmer has written the conditional expression not only to perform the test but also to do the work.

Thinking in C++
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   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire