Chapter 10 - Character Strings
Array of Characters
char word[] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ‘!’ };
word[0]
word[1]
word[2]
word[3]
word[4]
word[5]
'H'
'e'
'l'
'l'
'o'
'!'
Program 10.1
/*
* Function to concatenate two character strings
*/
#include <stdio.h>
concat (char result[], char str1[], int n1, char str2[], int n2)
{
int i;
// copy str1 to result
for (i = 0; i < n1; i++)
result[i] = str1[i];
for (i = 0; i < n2; i++)
result[n1 + i] = str2[i];
}
Program 10.1 (continued)
main()
{
char s1[5] = {'T', 'e', 's', 't', ' '};
char s2[6] = {'w', 'o', 'r', 'k', 's', '.'};
char s3[11];
int i;
concat (s3, s1, 5, s2, 6);
for (i = 0; i < 11; i++)
printf("%c", s3[i]);
printf ("\n");
system ("PAUSE");
}
Program 10.1 Output
Variable Length Character Strings
char word[] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ‘!’, ‘\0’ };
word[0]
word[1]
word[2]
word[3]
word[4]
word[5]
word[6]
'H'
'e'
'l'
'l'
'o'
'!'
'\0'
NULL Character
Terminates a String
Program 10.2
/*
* Function to count the number of characters in a string
*/
#include <stdio.h>
int string_length (char string[])
{
int count = 0;
while(string[count] != '\0')
count++;
return (count);
}
Program 10.2 (continued)
main()
{
char word1[] = {'a', 's', 't', 'e', 'r', '\0'};
char word2[] = {'a', 't', '\0'};
char word3[] = {'a', 'w', 'e', '\0'};
int i;
printf ("%i %i %i\n", string_length (word1), string_length (word2),
string_length (word3));
system ("PAUSE");
}
Program 10.2 Output
Initializing and Displaying Character Strings
char word[] = “Hello!”;
These Statements
Are Equivalent
char word[] = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ‘!’, ‘\0’ };
char word[7] = “Hello!”;
char word[6] = “Hello!”;
Leave Room for the
NULL Character
Program 10.3
/*
* Function to concatenate two character strings
*/
#include <stdio.h>
concat (char result[], char str1[], char str2[])
{
int i;
int j;
// copy str1 to result
for (i = 0; str1[i] != '\0'; i++)
result[i] = str1[i];
for (j = 0; str2[j] != '\0'; j++)
result[i + j] = str2[j];
result[i+j] = '\0';
}
Program 10.3 (continued)
main()
{
char s1[] = "Test ";
char s2[] = "works.";
char s3[20];
concat (s3, s1, s2);
printf("%s\n", s3);
system ("PAUSE");
}
Program 10.3 Output
Testing Two Character Strings for Equality
Since the C Programming Language does not support a
data type of string we cannot directly test two strings to
see if they are equal with a statement such as
if ( string1 == string2 )
<string.h>
Program 10.4
/*
* Function to determine if two strings are equal
*/
#include <stdio.h>
#define TRUE 1
#define FALSE 0
int equal_strings (char s1[], char s2[])
{
int i = 0;
while ((s1[i] == s2[i]) && (s1[i] != '\0') && (s2[i] != '\0'))
i++;
if ((s1[i] == '\0') && (s2[i] == '\0'))
return(TRUE);
else
return(FALSE);
}
Program 10.4 (continued)
main()
{
char stra[] = "string compare test";
char strb[] = "string";
printf ("%i\n", equal_strings (stra, strb));
printf ("%i\n", equal_strings (stra, stra));
printf ("%i\n", equal_strings (strb, "string"));
system ("PAUSE");
}
Program 10.4 Output
Inputting Character Strings
char string[81];
scanf ( “%s”, string);
char s1[81], s2[81], s3[81];
scanf ( “%s%s%s”, s1, s2, s3);
Program 10.5
/*
* Program to illustrate the %s scanf format characters
*/
#include <stdio.h>
main()
{
char s1[81];
char s2[81];
char s3[81];
printf ("Enter text:\n");
scanf ("%s%s%s", s1, s2, s3);
printf ("\ns1 = %s\ns2 = %s\ns3 = %s\n", s1, s2, s3);
system ("PAUSE");
}
Program 10.5 Output
Program 10.6
/*
* Function to read a line of text from a terminal
*/
#include <stdio.h>
read_line (char buffer[])
{
char character;
int i = 0;
do
{
character = getchar();
buffer[i] = character;
i++;
} while (character != '\n');
buffer[i-1] = '\0';
}
Program 10.6 (continued)
main()
{
char line[81];
int i;
for (i=0; i < 3; i++)
{
read_line(line);
printf ("%s\n\n", line);
}
system ("PAUSE");
}
Program 10.6 Output
Program 10.7
#include <stdio.h>
#define TRUE 1
#define FALSE 0
/*
* Function to determine if a character is alphabetic
*/
alphabetic (char c)
{
if (('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z'))
return (TRUE);
else
return (FALSE);
}
Program 10.7 (continued)
/*
* Function to count the number of words in a string
*/
count_words (char string[])
{
int looking_for_word = TRUE;
int word_count = 0;
int i;
for (i=0; string[i] != '\0'; i++)
{
if (alphabetic(string[i]))
{
if (looking_for_word)
{
word_count++;
looking_for_word = FALSE;
}
}
else
looking_for_word = TRUE;
}
return (word_count);
}
Program 10.7 (continued)
main()
{
char text1[] = "Well, here goes.";
char text2[] = "And here we go... again.";
printf ("%s - words = %i\n", text1, count_words (text1));
printf ("%s - words = %i\n", text2, count_words (text2));
system ("PAUSE");
}
Program 10.7 Output
Execution of count_words Function
i
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
string[i]
word_count
looking_for_word
'W'
'e'
'l'
'l'
','
‘ '
'h'
'e'
'r'
'e'
‘ '
'g'
'o'
'e'
's'
'.'
'\0'
0
1
1
1
1
1
1
2
2
2
2
2
3
3
3
3
3
3
1
0
0
0
0
1
1
0
0
0
0
1
0
0
0
0
1
1
The NULL String
A Character String that contains no characters other than
the NULL Character has a special name in the C
Programming Language, it is called the NULL String. The
string length will correctly return 0.
char buffer[100] = “”;
Program 10.8
#include <stdio.h>
#define TRUE 1
#define FALSE 0
/***** Insert alphabetic function here
*****/
/***** Insert read_line function here
*****/
/***** Insert count_words function here *****/
Program 10.8 (continued)
main()
{
char text[81];
int end_of_text = 0;
int total_words = 0;
printf ("Type in your text.\n");
printf ("When you are done, press 'RETURN'.\n\n");
while (!end_of_text)
{
read_line (text);
if (text[0] == '\0')
end_of_text = TRUE;
else
total_words += count_words (text);
}
printf("\nThere are %i words in the above text.\n", total_words);
system ("PAUSE");
}
Program 10.8 Output
Escape Characters
Escape Character
\a
\b
\f
\n
\r
\t
\v
\\
\”
\'
\?
\nnn
\xnn
Name
audible alert
backspace
form feed
newline
carriage return
horizontal tab
vertical tab
backslash
double quote
single quote
question mark
octal character value nnn
hexadecimal character value nn
More on Constant Strings
If you put a backslash character at the very end of the line and
followed it immediately by a carriage return, it will tell the C
Compiler to ignore the end of line. This line continuation
technique is used primarily for continuing long constant character
strings.
char letters[] = “abcdefghijklmnopqrstuvwxyz\
ABCDEFGHIJKLMNOPQRSTUVWXYZ”;
An even easier way of breaking up long character strings is to
divide them into two or more adjacent strings.
char letters[] = “abcdefghijklmnopqrstuvwxyz”
“ABCDEFGHIJKLMNOPQRSTUVWXYZ”;
Character Strings, Structures, and Arrays
Suppose we wanted to write a computer program that
acted as a dictionary. One of the first thoughts would be
to representation of the word and it definition. Since the
word and its definition are logically related, the notion of
a structure comes immediately to mind.
struct entry
{
char word[10];
char definition[50];
};
struct entry dictionary[100];
Program 10.9
/*
* Dictionary lookup program
*/
#include <stdio.h>
#define TRUE 1
#define FALSE 0
struct entry
{
char word[10];
char definition[50];
};
/***** Insert equal_string function here *****/
Program 10.9
/*
* Function to lookup a word inside a dictionary
*/
int lookup (struct entry dictionary[], char search [], int entries)
{
int i;
for (i=0; i < entries; i++)
if (equal_strings (search, dictionary[i].word))
return (i);
return (-1);
}
Program 10.9
main()
{
struct entry dictionary[100] = {
{ "aardvark", "a burrowing African mammal"
{ "abyss",
"a bottomless pit"
{ "acumen", "mentally sharp; keen"
{ "addle",
"to become confused"
{ "aerie",
"a high nest"
{ "affix",
"to append; attach"
{ "agar",
"a jelly made from seaweed"
{ "ahoy",
"a nautical call of greeting"
{ "aigrette", "an ornamental cluster of feathers"
{ "ajar",
"partially opened"
char word[10];
int entries = 10;
int entry_number;
},
},
},
},
},
},
},
},
},
} };
Program 10.9
printf("Enter word: ");
scanf("%9s", word);
entry_number = lookup (dictionary, word, entries);
if (entry_number != -1)
printf ("%s\n", dictionary[entry_number].definition);
else
printf ("Sorry, that word is not in my dictionary.\n");
system ("PAUSE");
}
Program 10.9 Output
A Better Search Method
Binary Search Algorithm
Step 1:
Set low to 0, high to n – 1
Step2:
If low > high, x does not exist in M and the
algorithm terminates
Step 3:
Set mid to (low + high) / 2
Step 4:
if M[mid] < x, set low to mid +1 and go to Step 2
Step 5:
if M[mid] > x, set high to mid -1 and go to Step 2
Step 6:
M[mid] equals x and the algorithm terminates
Binary Search Algorithm
/*
* Binary Search Algorithm
*/
int lookup (struct entry M[], char x[], int n)
{
int low = 0;
int high = n - 1;
int mid;
int result;
/* Step 1: */
/* Step 1: */
while (low <= high)
{
mid = (low + high) / 2;
/* Step 3: */
result = compare_strings (M[mid].word, x);
if (result == -1)
low = mid + 1;
/* Step 4: */
else if (result == 1)
high = mid - 1;
/* Step 5: */
else
return (mid);
/* Step 6: */
}
return (-1);
/* Step 2: */
}
Examples of Binary Search
Examples of Binary Search
Examples of Binary Search
Program 10.10
/*
* Dictionary lookup program
*/
#include <stdio.h>
struct entry
{
char word[10];
char definition[50];
};
Program 10.10 (continued)
/*
* Function to compare two character strings
*/
int compare_strings (char s1[], char s2[])
{
int i = 0;
while ((s1[i] == s2[i]) && (s1[i] != '\0') && (s2[i] != '\0'))
i++;
if (s1[i] < s2[i] )
/* s1 < s2 */
return(-1);
else if (s1[i] == s2[i]) /* s1 == s2 */
return (0);
else
/* s1 > s2 */
return(+1);
}
Program 10.10 (continued)
/*
* Function to lookup a word inside a dictionary
*/
int lookup (struct entry dictionary[], char search [], int entries)
{
int low = 0;
int high = entries - 1;
int mid;
int result;
while (low <= high)
{
mid = (low + high) / 2;
result = compare_strings (dictionary[mid].word, search);
if (result == -1)
low = mid + 1;
else if (result == 1)
high = mid - 1;
else
return (mid); /* found it */
}
return (-1); /* not found */
}
Program 10.10 (continued)
main()
{
struct entry dictionary[100] = {
{ "aardvark", "a burrowing African mammal"
{ "abyss",
"a bottomless pit"
{ "acumen", "mentally sharp; keen"
{ "addle",
"to become confused"
{ "aerie",
"a high nest"
{ "affix",
"to append; attach"
{ "agar",
"a jelly made from seaweed"
{ "ahoy",
"a nautical call of greeting"
{ "aigrette", "an ornamental cluster of feathers"
{ "ajar",
"partially opened"
char word[10];
int entries = 10;
int entry_number;
},
},
},
},
},
},
},
},
},
} };
Program 10.10 (continued)
printf("Enter word: ");
scanf("%9s", word);
entry_number = lookup (dictionary, word, entries);
if (entry_number != -1)
printf ("%s\n", dictionary[entry_number].definition);
else
printf ("Sorry, that word is not in my dictionary.\n");
system ("PAUSE");
}
Program 10.10 Output
Program 10.10 Output (Rerun)
ASCII Character Table
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
0
1
2
3
4
5
6
7
10
11
12
13
14
15
16
17
20
21
22
23
24
25
26
27
30
31
32
33
34
35
36
37
40
41
42
43
44
45
46
47
50
51
52
53
54
55
56
57
60
61
62
63
64
65
66
67
70
71
72
73
74
75
76
77
00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
12
13
14
15
16
17
18
19
1A
1B
1C
1D
1E
1F
20
21
22
23
24
25
26
27
28
29
2A
2B
2C
2D
2E
2F
30
31
32
33
34
35
36
37
38
39
3A
3B
3C
3D
3E
3F
0000 0000
0000 0001
0000 0010
0000 0011
0000 0100
0000 0101
0000 0110
0000 0111
0000 1000
0000 1001
0000 1010
0000 1011
0000 1100
0000 1101
0000 1110
0000 1111
0001 0000
0001 0001
0001 0010
0001 0011
0001 0100
0001 0101
0001 0110
0001 0111
0001 1000
0001 1001
0001 1010
0001 1011
0001 1100
0001 1101
0001 1110
0001 1111
0010 0000
0010 0001
0010 0010
0010 0011
0010 0100
0010 0101
0010 0110
0010 0111
0010 1000
0010 1001
0010 1010
0010 1011
0010 1100
0010 1101
0010 1110
0010 1111
0011 0000
0011 0001
0011 0010
0011 0011
0011 0100
0011 0101
0011 0110
0011 0111
0011 1000
0011 1001
0011 1010
0011 1011
0011 1100
0011 1101
0011 1110
0011 1111
NUL
SOH
STX
ETX
EOT
ENQ
ACK
BEL
BS
HT
LF
VT
FF
CR
SO
SI
DLE
DC1
DC2
DC3
DC4
NAK
SYN
ETB
CAN
EM
SUB
ESC
FS
GS
RS
US
SP
!
"
#
$
%
&
'
(
)
*
+
,
.
/
0
1
2
3
4
5
6
7
8
9
:
;
<
=
>
?
(Null char.)
(Start of Header)
(Start of Text)
(End of Text)
(End of Transmission)
(Enquiry)
(Acknowledgment)
(Bell)
(Backspace)
(Horizontal Tab)
(Line Feed)
(Vertical Tab)
(Form Feed)
(Carriage Return)
(Shift Out)
(Shift In)
(Data Link Escape)
(XON) (Device Control 1)
(Device Control 2)
(XOFF)(Device Control 3)
(Device Control 4)
(Negativ Acknowledgemnt)
(Synchronous Idle)
(End of Trans. Block)
(Cancel)
(End of Medium)
(Substitute)
(Escape)
(File Separator)
(Group Separator)
(Reqst to Send)(Rec. Sep.)
(Unit Separator)
(Space)
(exclamation mark)
(double quote)
(number sign)
(dollar sign)
(percent)
(ampersand)
(single quote)
(left/open parenthesis)
(right/closing parenth.)
(asterisk)
(plus)
(comma)
(minus or dash)
(dot)
(forward slash)
(colon)
(semi-colon)
(less than)
(equal sign)
(greater than)
(question mark)
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
100
101
102
103
104
105
106
107
110
111
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130
131
132
133
134
135
136
137
140
141
142
143
144
145
146
147
150
151
152
153
154
155
156
157
160
161
162
163
164
165
166
167
170
171
172
173
174
175
176
177
40
41
42
43
44
45
46
47
48
49
4A
4B
4C
4D
4E
4F
50
51
52
53
54
55
56
57
58
59
5A
5B
5C
5D
5E
5F
60
61
62
63
64
65
66
67
68
69
6A
6B
6C
6D
6E
6F
70
71
72
73
74
75
76
77
78
79
7A
7B
7C
7D
7E
7F
0100 0000
0100 0001
0100 0010
0100 0011
0100 0100
0100 0101
0100 0110
0100 0111
0100 1000
0100 1001
0100 1010
0100 1011
0100 1100
0100 1101
0100 1110
0100 1111
0101 0000
0101 0001
0101 0010
0101 0011
0101 0100
0101 0101
0101 0110
0101 0111
0101 1000
0101 1001
0101 1010
0101 1011
0101 1100
0101 1101
0101 1110
0101 1111
0110 0000
0110 0001
0110 0010
0110 0011
0110 0100
0110 0101
0110 0110
0110 0111
0110 1000
0110 1001
0110 1010
0110 1011
0110 1100
0110 1101
0110 1110
0110 1111
0111 0000
0111 0001
0111 0010
0111 0011
0111 0100
0111 0101
0111 0110
0111 0111
0111 1000
0111 1001
0111 1010
0111 1011
0111 1100
0111 1101
0111 1110
0111 1111
@
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
[
\
]
^
_
`
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
{
|
}
~
DEL
(AT symbol)
(left/opening bracket)
(back slash)
(right/closing bracket)
(caret/circumflex)
(underscore)
(left/opening brace)
(vertical bar)
(right/closing brace)
(tilde)
(delete)
ASCII Alphabetic Characters
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
101
102
103
104
105
106
107
110
111
112
113
114
115
116
117
120
121
122
123
124
125
126
127
130
131
132
41
42
43
44
45
46
47
48
49
4A
4B
4C
4D
4E
4F
50
51
52
53
54
55
56
57
58
59
5A
0100 0001
0100 0010
0100 0011
0100 0100
0100 0101
0100 0110
0100 0111
0100 1000
0100 1001
0100 1010
0100 1011
0100 1100
0100 1101
0100 1110
0100 1111
0101 0000
0101 0001
0101 0010
0101 0011
0101 0100
0101 0101
0101 0110
0101 0111
0101 1000
0101 1001
0101 1010
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
141
142
143
144
145
146
147
150
151
152
153
154
155
156
157
160
161
162
163
164
165
166
167
170
171
172
61
62
63
64
65
66
67
68
69
6A
6B
6C
6D
6E
6F
70
71
72
73
74
75
76
77
78
79
7A
0110 0001
0110 0010
0110 0011
0110 0100
0110 0101
0110 0110
0110 0111
0110 1000
0110 1001
0110 1010
0110 1011
0110 1100
0110 1101
0110 1110
0110 1111
0111 0000
0111 0001
0111 0010
0111 0011
0111 0100
0111 0101
0111 0110
0111 0111
0111 1000
0111 1001
0111 1010
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
Character Operations
Whenever a character constant or variable is used in an
expression, it is automatically converted to, and
subsequently treated as, an integer value. For example,
(‘a’ <= c) && (c <= ‘z’)
(97 <= c) && (c <= 122)
ASCII Numeric Characters
48
60
30
0011 0000
0
49
61
31
0011 0001
1
50
62
32
0011 0010
2
51
63
33
0011 0011
3
52
64
34
0011 0100
4
53
65
35
0011 0101
5
54
66
36
0011 0110
6
55
67
37
0011 0111
7
56
70
38
0011 1000
8
57
71
39
0011 1001
9
Character Operations
Suppose the character variable c contained one of the
characters ‘0’ thru ‘9’ and the we wished to convert this
value into the corresponding integer 0 thru 9. Since the
digits of virtually all character sets are represented by
sequential integer values, we can easily convert c into its
integer equivalent by subtracting the character constant
‘0’ from it. For example,
char c = ‘5’;
int i = c – ‘0’;
c = 53;
i = 53 – 48;
Program 10.11
/*
* Function to convert a string to an integer
*/
#include <stdio.h>
int string_to_integer (char string[])
{
int integer_value;
int result = 0;
int i = 0;
for (i=0; ('0' <= string[i]) && (string[i] <= '9'); i++)
{
integer_value = string[i] - '0';
result = result *10 + integer_value;
}
return(result);
}
Program 10.11 (continued)
main()
{
printf ("%i\n", string_to_integer ("245"));
printf ("%i\n", string_to_integer ("100") + 25);
printf ("%i\n", string_to_integer ("13x5"));
system ("PAUSE");
}
Program 10.11 Output