Teach Yourself Borland C++ in 14 Days - portal

48 Day 2
Now that you’ve seen the for loop in action, it won’t be too difficult to apply the same
concepts to the while and do-while loops. Let’s take a look at those now.
The while Loop
The while loop differs from the for loop in that it contains only a test condition that is
checked at the start of each iteration. As long as the test condition is true, the loop keeps
running. Here’s an example:
int x;
while (x < 1000) {
x = DoSomeCalculation();
}
In this example I am calling a function that I assume will eventually return a value greater than
1,000. As long as the return value from this function is less than 1,000, the while loop
continues to run. When the variable x contains a value greater than or equal to 1,000, the test
condition yields false, and program execution jumps to the first line following the while
loop’s ending brace. A common implementation of a while loop uses a bool as a test variable.
The state of the test variable can be set somewhere within the body of the loop:
bool done = false;
while (!done) {
// some code here
done = SomeFunctionReturningABool();
// more code
}
At some point it is expected that the variable done will be false and the loop will terminate.
The program in Listing 2.2 illustrates the use of the while loop.
Listing 2.2. WHILETST.CPP.
1: #include
2: #include
3: #pragma hdrstop
4: int main(int argv, char** argc)
5: {
6: cout