Char and Int Conversion, Ordering of Characters

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September 19, 2023 (05:11:10 PM)

This lab serves multiple goals:

Warm Up

Characters are represented by integers: you can read on wikipedia a mapping between the glyphs (e.g., space, A, !, etc.) and decimal values, to be read as “integer code” (e.g., 32, 33, 34, etc.).

In the referenced table on wikipedia, each character’s integer code is given for different numeral systems:

The decimal system is what we use every day, but computer programs occasionally use other numerical systems. For that system, it gives (no need to memorize this information, this is simply for your general awareness):

Decimal representation Glyph (character)
32 space
33 !
34
35 #
36 $
37 %
38 &
39
40 (
41 )
42 *
43 +
44 ,
45 -
46 .
47 /
48 0
49 1
50 2
51 3
52 4
53 5
54 6
55 7
56 8
57 9
58 :
59 ;
60 <
61 =
62 >
63 ?
64 @
65 A
66 B
67 C
68 D
69 E
70 F
71 G
72 H
73 I
74 J
75 K
76 L
77 M
78 N
79 O
80 P
81 Q
82 R
83 S
84 T
85 U
86 V
87 W
88 X
89 Y
90 Z
91 [
92 \
93 ]
94 ^
95 _
96 `
97 a
98 b
99 c
100 d
101 e
102 f
103 g
104 h
105 i
106 j
107 k
108 l
109 m
110 n
111 o
112 p
113 q
114 r
115 s
116 t
117 u
118 v
119 w
120 x
121 y
122 z
123 {
124 |
125 }
126 ~

Note that the characters are divided into groups and that there are 95 printable characters.

Converting Between Characters Representations

Copy the following snippet of code in a Main method:

int intVar = (int)'C';
char charVar = (char)84;
Console.WriteLine($"'C' is represented as {intVar}");
Console.WriteLine($"{charVar} corresponds to the value 84"); 

And note that we can explicitly convert int into char, and char into int, but the conversion from char to int could be done implicitly by C#; replace the previous first line with:

int intVar = 'C';

and note that your program still compiles.

Can you also convert implicitly int into char?

Next, write code to determine the int values for the following characters:

char value int value
w 119
A
5
#

Also determine what characters the following integers (in the decimal system) represent:

int value char value
49
104
89
Solution:

Your code could look like the following:

Console.WriteLine("int value | char value\n" +
  "--------- | ---------\n" +
  (int)'w' + "       | w\n" +
  (int)'A' + "        | A\n" +
  (int)'5' + "        | 5\n" +
  (int)'#' + "        | #\n" +
  "--------- | ---------\n" +
  "49        | " + (char)49 + "\n" +
  "104       | " + (char)104 + "\n" +
  "89        | " + (char)89 + "\n"
);

Testing for Equality

You can test if a character is equal to another by using ==, as for integer values. This is particularly useful when we want to ask the user for a “yes” / “no” decision.

Write a program that

Solution:

You can get started with this short program:

Console.WriteLine("Enter a character:");
// We ask the user for a character.
char input = Console.ReadKey().KeyChar;
// We read from the user.
Console.WriteLine();
// We are introducing a new line after the user input
if (input == 'Y')
{
    // The input is the letter Y, uppercase.
    Console.WriteLine("You entered 'Y'.");
}

It does not fit the description, though, as many elements are missing. Implement them all!

Comparing

Exactly as 65 is less than 97, the character associated with 65, A, is less than the character associated with 97, a.

You can convince yourself by executing the following code:

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

that displays “‘A’ is less than ‘a’.”.

Implement the following short program to practice this concept.

  1. Ask the user to enter a lowercase character.

  2. Check that the character is within the a - z range (it is a lowercase character),

  3. When it is not in this range, display “The character ‘X’ is not a lowercase character”, where X is replaced by the character they entered,

  4. Otherwise, perform the following steps:

    • if the user enters character 'n', display “You entered ‘n’.”
    • if the character occurs before 'n', display “The character you entered is a lowercase letter before ‘n’.”
    • if the character occurs after 'n', display “The character you entered is a lowercase letter after ‘n’.”
Solution:

The following short program fits the description:

 Console.WriteLine("Enter a character:");
// We ask the user for a character.
char input = Console.ReadKey().KeyChar;
// We read from the user.
Console.WriteLine();
// We are introducing a new line after the user input
if (input >= 'a' && input <= 'z')
{
   // The input is a lowercase letter.
   if (input == 'n') { Console.WriteLine("You entered 'n'."); }
   else if (input < 'n') { Console.WriteLine("The character you entered is a lower case letter before 'n'."); }
   else { Console.WriteLine("The character you entered is a lower case letter after 'n'."); }
}
else
{
   // The input is not a lowercase letter.
   Console.WriteLine("The character '" + input + "' is not a lowercase character.");
}

Pushing Further (Optional)

String Comparison

Comparing strings cannot be done with > and < operators (we can use ==, however). To compare them, we have to use the CompareOrdinal method of the String class.

It works as follows:

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 a string made of only one character, but we can compare arbitrarily complex strings:

if (String.CompareOrdinal("Augusta", "August") > 0) {
  Console.Write("\"Augusta\" is greater than \"August\".");
} else {
  Console.Write("\"Augusta\" is less than \"August\".");
}

To conclude with this topic, note that the integer returned actually has a precise value.

Examine the following code to understand it.

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?