Ada Engineering

Module 2 – Use types to describe valid data

Page 1 of 3 · About 15 minutes per lesson, including practice.

Give values a meaningful range

A type describes values and permitted operations. A subtype can narrow a type: a score in this exercise is an integer from zero through one hundred. Raw is deliberately a wider Integer so that we can represent input which is not yet trusted. The membership test asks whether that value belongs to Score before converting it.

with Ada.Text_IO;

procedure Main is
   subtype Score is Integer range 0 .. 100;
   Raw : Integer := 101;
begin
   if Raw in Score then
      Ada.Text_IO.Put_Line ("Accepted" & Score'Image (Score (Raw)));
   else
      Ada.Text_IO.Put_Line ("Score must be between 0 and 100");
   end if;
end Main;

With Raw = 101, the example prints the range message. Change it to 100 and predict the accepted message. Score'Image produces a string; for nonnegative integer values, the image includes a leading space. Treat formatting and correctness as separate questions.

Reference: AdaCore: types and ranges.

Example code on Agila Forge ↗