integer - Manipulating hexadecimal numbers in Pascal

Question

I'm currently reading up on binary and hexadecimal number manipulation and I'm finding it difficult to complete a task and was wondering if anyone can help clarify this question for me.

I have a hexadecimal number '04831037' and I need to replace the first number (0) with a '1' via a Pascal program. I'm not sure how to go about doing this.

I know how to convert an integer into a hexadecimal value via:

var 
  iNumber : Integer;

begin
  iNumber := 75698231;
  writeln(IntToHex(iNumber, 8));
end.

> Output: 04831037

But now I am confused on how to replace a single number in the output. Any help would be greatly appreciated

Answer 1

Hexadecimal numbers are of base 16, i.e. each digit represents a value 0..15.

To form a value of ex. 16, i.e. $10 following expression could be used: (Note: the $ sign means that the value is a hexadecimal value)

16 = $10 = 1*16¹ + 0*16⁰

The value 28 ($1C) is expressed by:

28 = $1C = 1*16¹ + 12*16⁰

To add $10000000 to a number, use

$10000000 = 1*16⁷

In code that would look like:

iNumber := iNumber + $10000000; 

---

Lets look at the question:

I have a hexadecimal number '04831037' and I need to replace the first number (0) with a '1'

This means you will first subtract the number with $00000000 and then add $10000000.

In code that would be:

iNumber := $04831037;
iNumber := iNumber - $00000000 + $10000000;
WriteLn(IntToHex(iNumber,8)); // Writes '14831037'