Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 5 ■ Programs with Repetition Logic
While this will work, we can express it a bit neater using a do...while statement.
The general form of the do...while statement in C is
do
<statement>
while (<expression>);
The words do and while, the brackets, and the semicolon are required. You must supply
<statement> and <expression>.
When a do...while is encountered,
1. <statement> is executed
2. <expression> is then evaluated; if it is true (non-zero), repeat from step
1. If it is false (zero), execution continues with the statement, if any, after
the semicolon.
As long as <expression> is true, <statement> is executed. It is important to note that because
of the way the construct is written, <statement> is always executed at least once.
Using do...while, we can express the logic above as follows:
do {
printf("Enter a day of the week (1-7): ");
scanf("%d", &day);
} while (day < 1 || day > 7); //as long as day is invalid
Note how much neater this looks. Here, <statement> is the block delimited by { and }, and
<expression> is day < 1 || day > 7.
We illustrate the use of do...while with two more examples.
5.15.1 Highest Common Factor
Previously, we wrote Program P5.2 to find the HCF of two integers using Euclid's algorithm. We
now rewrite the program using do...while to ensure that the two numbers entered are indeed
positive integers. We also re-code the algorithm using do...while instead of while. This is shown
as Program P5.17.
133
www.it-ebooks.info