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ASCII Table & Codes

Instructor: Martin Gibbs

Martin has 16 years experience in Human Resources Information Systems and has a PhD in Information Technology Management. He is an adjunct professor of computer science and computer programming.

A computer doesn't see characters like we do. Instead, it uses codes to represent these values. The most common code standard is ASCII. This lesson will discuss the ASCII table and the set of codes it contains.

ASCII

At its most basic level, a computer only understands 1s and 0s. These are called bits - 8 of them make up a byte.

In many software applications, or in programming languages like Java, a byte can only hold a positive number value. The largest value allowed is 255. So if a computer only knows numbers for characters, how do you get it to display a Z or an N?

Here's where ASCII to the rescue! Numeric bytes are interpreted as human-readable characters. ASCII stands for the American Standard Code for Information Interchange. It is a character set that holds numeric codes to represent characters.

The first ASCII tables only held values from 0 to 127. However, since the value is stored in a byte, the real upper bound is 256. This extended the table to 255. Why not 256? Remember that we have to count the 0! You still get 256 values.

Letters, numbers and special characters are all given a code in the set. For example, 'A' is represented by 65. Sometimes you'll see representations of ASCII tables that included the leading 0. For example, 065. This is perfectly valid and really just a formatting style of the table itself.

But Is It a Character or a Byte?

It's both! Don't worry if you're confused. ASCII codes are characters that are one byte long. However, it is still a character.

ASCII Tables

Let's take a look at the ASCII table. We'll make it readable by breaking it up into sections. The table does actually start at 0 (0 being a NULL or empty character, not space!). However, the codes before 32 are called non-printing characters. They are leftovers from legacy computer systems and are not used much anymore.

Symbols

ASCII Code Value Notes
32 (space)
33 !
34 ' (Quotation mark)
35 # (Number sign)
36 $ (Dollar sign)
37 % (Percent sign)
38 & (Ampersand)
39 ' (Apostrophe)
40 ( (round brackets or parentheses)
41 ) (round brackets or parentheses)
42 * (Asterisk)
43 + (Plus sign)
44 , (Comma)
45 - (Hyphen)
46 . (Full stop, dot)
47 / (Slash)

Numbers

The next table shows the ASCII codes for numbers and numerical symbols:

ASCII Code Value Notes
48 0
49 1
50 2
51 3
52 4
53 5
54 6
55 7
56 8
57 9
58 : (Colon)
59 ; (Semicolon)
60 < (Less-than sign)
61 = (Equals sign)
62 > (Greater-than sign, Inequality)
63 ? (Question mark)
64 @ (At sign)

Upper-Case Letters

Next we have the table for upper-case letters.

ASCII Code Value Notes
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

More Symbols and Lower-Case Letters

Between the upper and lower case codes we have some more symbols. Following this are the lower case letter codes.

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