While statement

We saw an example using a while loop, in the initial introduction to Ada.

Statement form:

	while test loop
		statement(s);
	end loop;

While loops may be designed as a repeat structure, to execute at least once

• example (to ensure you have a positive value of j)

	j := -1;
	while (j < 0) loop
		PUT("Enter positive j: "); GET(j); SKIP_LINE;
	end loop;

• example (to test when finished)

	tot := 0;
	PUT("Enter j (-1 to exit): "); GET(j); SKIP_LINE;
	while (j /= -1) loop
		tot := tot + j;
		PUT("Enter j (-1 to exit): "); GET(j); SKIP_LINE;
	end loop;
	PUT("Total is "); PUT(tot); NEW_LINE;

An example program shows the use of a while loop when a user is being asked to answer 'Y' or 'N' to a question. The loop executes continually until a suitable value is typed by the user.

Rules for while statements

• test is an expression which evaluates as either true or false (as in if statements)
• the statement(s) may be any Ada statements
• the entire while structure (from while to end loop) is a single Ada statement, terminated by a ;

Style Rules for while statements

• statement(s) inside the while are indented by a constant amount
• the end loop is required, and should be at the same indent as the corresponding while

Semantics of while statement

while != if