Calculating factorial numbers

user_7369299 0
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I am self-teaching myself the Ada Programming language and in the text book I am using there is an exercise to print out the factorial value of a number entered by the user. My program compiles and does run fine and I do get the expected output, but if I type in the value of 13, the program crashes and raises an error.

I have no idea why the number 13 does this. Is it an error with the IDE (I use GNAT Studio) and I currently use the Ada 2012 standard. Here is my code:

with Ada.Text_IO;
use Ada.Text_IO;
with Ada.Integer_Text_IO;
use Ada.Integer_Text_IO;

-- procedure main - begins the program
procedure main is
   counter : Integer := 1;
   number : Integer := 0;
   factorial : Integer := 1;
begin
   New_Line;
   
   while counter <= 5 loop
      Put("Enter an integer: ");
      Get(number);
      
      for Count in 1 .. number loop
         factorial := factorial * Count;
      end loop;
      
      Put_Line("Factorial value is: " & integer'image(factorial));
      factorial := 1;
      
      counter := counter + 1;
   end loop;
   
   New_Line;
end main; -- end procedure main

Error Message is this: raised CONSTRAINT_ERROR : main.adb:35 overflow check failed [2021-04-11 13:25:10] process exited with status 1, elapsed time: 02.07s

It seems like such a small issue, but I would just be interested to know if there is something wrong with the code that is creating this, or is it just a general bug with the software I use.

Thank you in advance.

ada
1 Answers

Factorial of 12 is 479,001,600. Multiply by 13 to get factorial of 13, and the value is 6,227,020,800 which is larger than can fit in a 32-bit binary number.

So the Constraint_Error is telling you that the type Integer cannot represent factorial of 13 -- the computation overflowed. If you want to compute larger factorials, you must use a "wider" integer type. Note that the width of Integer is compiler-specific, although guaranteed to be at least 16 bits. Some other compiler might use 64-bit Integers. Normal advice for Ada is to define your own integer types (type XX is range 0 .. 83838 or whatever) depending on what you need.

Otherwise your program looks ok, from the Ada point of view.

user_150040770
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