---
title: CSCI 1301 -- Lab 21
author: Clément Aubert
lang: en
fontsize: 10pt
documentclass: scrartcl
numbersections: true
links-as-notes: true
papersize: letter
geometry: margin=1in
keywords:
- Computer Science
- Problem solving methods
- Syllabus
- Augusta University
- Bachelor of Science
---

# Char and Int Conversion, Ordering of Characters

## Reading and Understanding

Characters are represented by integers: cf. <https://en.wikipedia.org/wiki/ASCII#Printable_characters> for a mapping between the glyphs (i.e., space, !, etc.) and **dec**imal values (to be read as "integer code", i.e., 32, 33, 34, etc.).
Note that the characters are divided in groups, and that there are 95 printable characters.

## Converting

Copy the following snippet of code in a `Main` method:

~~~~~~~{.cs .numberLines .lineAnchors}
int intVar = (int)'C';
char charVar = (char)84;
Console.WriteLine($"'C' is represented as {intVar}\n"
    + $"{charVar} corresponds to the value 84"); 
~~~~~~~

And note that we can explicitely convert `int` into `char`, and `char` into `int`.

Actually, the conversion from `char` to `int` could be done implicitely by C#: replace the previous first line with

~~~~~~~{.cs}
int intVar = 'C';
~~~~~~~

And note that your program would still compile.
Can you also convert implicitely `int` into `char`?

## Comparing

Exactly as $65$ is less than $97$, the character associated  to $65$, `A`, is less than the character associated with $97$, `a`.
You can convince yourself by executing the following code:

~~~~~~~{.cs}
if ('A' > 'a')
    Console.Write("A is greater than a");
else
    Console.Write("A is less than a");
~~~~~~~

## Testing for Equality

Note that you can also test if a character is equal to an other by using `==`, as for integer values.
This is particularly useful when we want to ask the user for a "yes" / "no" decision.

Write a snippet of code that 

- Ask the user for a character,
- Display on the screen "The user said yes" if the user entered "Y" or "y",
- Display on the screen "The user said no" if the user entered "N" or "n",
- Display on the screen "The user entered an incorrect value" if the user entered any other character.

To read *a single character* (instead of a whole string), use 

~~~~~~~{.cs}
Console.WriteLine("Press y or Y for Yes, n or N for No:");
char answer = Console.ReadKey().KeyChar;
~~~~~~~


# Pushing Further (Optionnal)

This lab's pushing further suggests to take some advance in two topics we will be covering soon: `for` loops and `string` comparison

## First `for` loop

Try to understand what the following code does:

~~~~~~~{.cs}
for (int i = 32; i <= 126; i++)
    Console.Write((char)i);
~~~~~~~

Compile it, execute it, understand what its purpose is, and what its structure is.

## String Comparison


Comparing strings cannot be done with `>` and `<` operators.
To compare them, we have to use the [CompareOrdinal](https://docs.microsoft.com/en-us/dotnet/api/system.string.compareordinal?view=netframework-4.7.1) method of the [String](https://msdn.microsoft.com/en-us/library/system.string(v=vs.110).aspx) class.
It works as follow:

~~~~~~~{.cs}
if (String.CompareOrdinal("A", "a") > 0)
{
    Console.Write("A is greater than a");
}
else
{
    Console.Write("A is less than a");
}
~~~~~~~

Note that `CompareOrdinal` returns an integer, that we then compare with $0$.

- If the value returned is $0$, then the strings are the same,
- If the value returned is less than $0$, then the first string is less than the second one,
- If the value returned is greater than $0$, then the first string is greater than the second one.

In the previous example, we tested string made of only one character, but we can compare arbitrarily complex strings:

~~~~~~~{.cs}
if (String.CompareOrdinal("Augusta", "Auguste") > 0)
{
    Console.Write("Augusta is greater than Auguste");
}
else
{
    Console.Write("Augsta is less than Auguste");
}
~~~~~~~

To conclude with this topic, note that the integer returned actually has a precise value: examine the following code to understand it.

~~~~~~~{.cs}
if (String.CompareOrdinal("A", "a") == ((int)'A' - (int)'a'))
    Console.WriteLine("Ok, I get it now");

if (String.CompareOrdinal("Ab", "az") == (((int)'A' + (int)'b') - ((int)'a' + (int)'z')))
    Console.WriteLine("Yes, I really do.");
else if (String.CompareOrdinal("Ab", "az") == ((int)'A' - (int)'a'))
    Console.WriteLine("Or do I?");
    
if (String.CompareOrdinal("ABCDEf", "ABCDEF") == (int)'f' - (int)'F')
    Console.WriteLine("Ok, now I'm good.");
~~~~~~~

Do you understand how the returning value is computed for these strings?
