ASCII table

In computer programs, we often manipulate characters that are stored in ASCII. The letter "a" is the value 97. And "b" is 98.

Notes on table

Some values in ASCII are represented with the string "control" or "whitespace." These are not easy to display in a web page file.

The table

There are 128 values in ASCII. This is a small subset of Unicode. 2 bytes are needed for Unicode, but ASCII requires just one byte.

' Decimal  ASCII      Hex
0 control 0
1 control 1
2 control 2
3 control 3
4 control 4
5 control 5
6 control 6
7 control 7
8 control 8
9 \t 9
10 \n a
11 whitespace b
12 \f c
13 \r d
14 control e
15 control f
16 control 10
17 control 11
18 control 12
19 control 13
20 control 14
21 control 15
22 control 16
23 control 17
24 control 18
25 control 19
26 control 1a
27 control 1b
28 whitespace 1c
29 whitespace 1d
30 whitespace 1e
31 whitespace 1f
32 space 20
33 ! 21
34 " 22
35 # 23
36 $ 24
37 % 25
38 & 26
39 ' 27
40 ( 28
41 ) 29
42 * 2a
43 + 2b
44 , 2c
45 - 2d
46 . 2e
47 / 2f
48 0 30
49 1 31
50 2 32
51 3 33
52 4 34
53 5 35
54 6 36
55 7 37
56 8 38
57 9 39
58 : 3a
59 ; 3b
60 < 3c
61 = 3d
62 > 3e
63 ? 3f
64 @ 40
65 A 41
66 B 42
67 C 43
68 D 44
69 E 45
70 F 46
71 G 47
72 H 48
73 I 49
74 J 4a
75 K 4b
76 L 4c
77 M 4d
78 N 4e
79 O 4f
80 P 50
81 Q 51
82 R 52
83 S 53
84 T 54
85 U 55
86 V 56
87 W 57
88 X 58
89 Y 59
90 Z 5a
91 [ 5b
92 \ 5c
93 ] 5d
94 ^ 5e
95 _ 5f
96 ` 60
97 a 61
98 b 62
99 c 63
100 d 64
101 e 65
102 f 66
103 g 67
104 h 68
105 i 69
106 j 6a
107 k 6b
108 l 6c
109 m 6d
110 n 6e
111 o 6f
112 p 70
113 q 71
114 r 72
115 s 73
116 t 74
117 u 75
118 v 76
119 w 77
120 x 78
121 y 79
122 z 7a
123 { 7b
124 | 7c
125 } 7d
126 ~ 7e
127 control 7f

Example program

Next we introduce the Java program that generated the above table. The program displays the header for the table, then loops through 128 values to display the rows.

public class Program {
    public static void main(String[] args) {

        // Write the header.
        System.out.printf("%1$-8s %2$-10s %3$s\n",
                "Decimal", "ASCII", "Hex");

        // Loop over all possible ASCII codes.
        int min = 0;
        int max = 128;
        for (int i = min; i < max; i++) {
            char c = (char) i;
            String display = "";
            // Figure out how to display whitespace.
            if (Character.isWhitespace(c)) {
                switch (c) {
                case '\t':
                    display = "\\t";
                    break;
                case ' ':
                    display = "space";
                    break;
                case '\n':
                    display = "\\n";
                    break;
                case '\r':
                    display = "\\r";
                    break;
                case '\f':
                    display = "\\f";
                    break;
                default:
                    display = "whitespace";
                    break;
                }
            } else if (Character.isISOControl(c)) {
                // Handle control chars.
                display = "control";
            } else {
                // Handle other chars.
                display = Character.toString(c);
            }
            // Write a string with padding.
            System.out.printf("%1$-8d %2$-10s %3$s\n",
                    i, display, Integer.toHexString(i));
        }
    }
}
See above table.

ASCII manipulation

We can discover optimizations by inspecting the ASCII table. For example, we can convert the letters "a" through "z" to 0-26 by subtracting 97.

Digit conversion

To convert from digit chars "0" through "9" to actual digits, we must subtract 48. This is a simple conversion.

Review

An ASCII table helps in many aspects of computer programming. We can develop optimizations with ASCII codes to improve program performance.