Chapter 10 – Characters, Strings, and the
string Class
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Starting Out with C++, 3rd Edition
10.1 Character Testing
• The C++ library provides several macros
for testing characters.
– Be sure to include ctype.h header file
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Table 10-1
Character
Macro
Description
isalpha
Returns true (a nonzero number) if the argument is a letter of the alphabet.
Returns 0 if the argument is not a letter.
isalnum
Returns true (a nonzero number) if the argument is a letter of the alphabet or a
digit. Otherwise it returns 0.
isdigit
Returns true (a nonzero number) if the argument is a digit 0–9. Otherwise it
returns 0.
islower
Returns true (a nonzero number) if the argument is a lowercase letter.
Otherwise, it returns 0.
isprint
Returns true (a nonzero number) if the argument is a printable character
(including a space). Returns 0 otherwise.
ispunct
Returns true (a nonzero number) if the argument is a printable character other
than a digit, letter, or space. Returns 0 otherwise.
isupper
Returns true (a nonzero number) if the argument is an uppercase letter.
Otherwise, it returns 0.
isspace
Returns true (a nonzero number) if the argument is a whitespace character.
Whitespace characters are any of the following:
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Program 10-1
// This program demonstrates some of the character testing
// functions.
#include <iostream.h>
#include <ctype.h>
void main(void)
{
char input;
cout << "Enter any character: ";
cin.get(input);
cout << "The character you entered is: " << input <<
endl;
cout << "Its ASCII code is: " << int(input) << endl;
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Program continues
if (isalpha(input))
cout << "That's an alphabetic character.\n";
if (isdigit(input))
cout << "That's a numeric digit.\n";
if (islower(input))
cout << "The letter you entered is lowercase.\n";
if (isupper(input))
cout << "The letter you entered is uppercase.\n";
if (isspace(input))
cout << "That's a whitespace character.\n";
}
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Program Output With Example input
Enter any character: A [Enter]
The character you entered is: A
Its ASCII code is: 65
That's an alphabetic character.
The letter you entered is uppercase.
Program Output With Other Example input
Enter any character: 7 [Enter]
The character you entered is: 7
Its ASCII code is: 55
That's a numeric digit.
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Program 10-2
// This program tests a customer number to determine if it is
// in the proper format.
#include <iostream.h>
#include <ctype.h>
// Function prototype
bool testNum(char []);
void main(void)
{
char customer[8];
cout << "Enter a customer number in the form ";
cout << "LLLNNNN\n";
cout << "(LLL = letters and NNNN = numbers): ";
cin.getline(customer, 8);
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Program continues
if (testNum(customer))
cout << "That's a valid customer number.\n";
else
{
cout << "That is not the proper format of the ";
cout << "customer number.\nHere is an example:\n";
cout << "
ABC1234\n";
}
}
// Definition of function testNum.
bool testNum(char custNum[])
{
// Test the first three characters for alphabetic letters
for (int count = 0; count < 3; count++)
{
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Program continues
if (!isalpha(custNum[count]))
return false;
}
// Test the last 4 characters for numeric digits
for (int count = 3; count < 7; count++)
{
if (!isdigit(custNum[count]))
return false;
}
return true;
}
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Program Output With Example input
Enter a customer number in the form LLLNNNN
(LLL = letters and NNNN = numbers): RQS4567 [Enter]
That's a valid customer number.
Program Output With Other Example input
Enter a customer number in the form LLLNNNN
(LLL = letters and NNNN = numbers): AX467T9 [Enter]
That is not the proper format of the customer number.
Here is an example:
ABC1234
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10.2 Character Case Conversion
• The C++ library offers functions for
converting a character to upper or lower
case.
– Be sure to include ctype.h header file
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Table 10-2
Function
Description
toupper
Returns the uppercase equivalent of its argument.
tolower
Returns the lowercase equivalent of its argument.
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Program 10-3
// This program calculates the area of a circle. It asks the
// user if he or she wishes to continue. A loop that
// demonstrates the toupper function repeats until the user
// enters 'y', 'Y', 'n', or 'N'.
#include <iostream.h>
#include <ctype.h>
void main(void)
{
const float pi = 3.14159;
float radius;
char go;
cout << "This program calculates the area of a circle.\n";
cout.precision(2);
cout.setf(ios::fixed);
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Program continues
do
{
cout << "Enter the circle's radius: ";
cin >> radius;
cout << "The area is " << (pi * radius * radius);
cout << endl;
do
{
cout << "Calculate another? (Y or N) ";
cin >> go;
} while (toupper(go) != 'Y' && toupper(go) != 'N');
} while (toupper(go) == 'Y');
}
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Program Output With Example input
This program calculates the area of a circle.
Enter the circle's radius: 10 [Enter]
The area is 314.16
Calculate another? (Y or N) b Enter]
Calculate another? (Y or N) y [Enter]
Enter the circle's radius: 1 [Enter]
The area is 3.14
Calculate another? (Y or N) n [Enter]
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10.3 Review of the Internal Storage of
C-strings
• A C-string is a sequence of characters stored
in consecutive memory locations,
terminated by a null character.
Figure 10-1
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Program 10-4
// This program contains string constants
#include <iostream.h>
void main(void)
{
char again;
do
{
cout << "C++ programming is great fun!" << endl;
cout << "Do you want to see the message again? ";
cin >> again;
} while (again == 'Y' || again == 'y');
}
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Program 10-5
// This program cycles through a character array, displaying
// each element until a null terminator is encountered.
#include <iostream.h>
void main(void)
{
char line[80];
int count = 0;
cout << "Enter a sentence of no more than 79
characters:\n";
cin.getline(line, 80);
cout << "The sentence you entered is:\n";
while (line[count] != '\0')
{
cout << line[count];
count++;
}
}
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Starting Out with C++, 3rd Edition
Program Output with Example input
Enter a sentence of no more than 79 characters:
C++ is challenging but fun! [Enter]
The sentence you entered is:
C++ is challenging but fun!
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Starting Out with C++, 3rd Edition
10.4 Library Functions for Working with
C-strings
• The C++ library has numerous functions for
handling C-strings These functions perform
various tests and manipulations.
• Functions discussed in this section require
the inclusion of string.h header file
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Figure 10-2
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Table 10-3
Function
strlen
strcat
strcpy
strncpy
strcmp
strstr
Description
Accepts a C-string or a pointer to a string as an argument. Returns the length of the
string (not including the null terminator. Example Usage: len = strlen(name);
Accepts two C-strings or pointers to two strings as arguments. The function appends
the contents of the second string to the first string. (The first string is altered, the
second string is left unchanged.) Example Usage: strcat(string1, string2);
Accepts two C-strings or pointers to two strings as arguments. The function copies
the second string to the first string. The second string is left unchanged. Example
Usage: strcpy(string1, string2);
Accepts two C-strings or pointers to two strings and an integer argument. The third
argument, an integer, indicates how many characters to copy from the second string
to the first string. If the string2 has fewer than n characters, string1 is padded with
'\0' characters. Example Usage: strncpy(string1, string2, n);
Accepts two C-strings or pointers to two string arguments. If string1 and string2are
the same, this function returns 0. If string2 is alphabetically greater than string1, it
returns a negative number. If string2 is alphabetically less than string1, it returns a
positive number. Example Usage: if (strcmp(string1, string2))
Accepts two C-strings or pointers to two C-strings as arguments, searches for the
first occurrence of string2 in string1. If an occurrence of string2 is found, the
function returns a pointer to it. Otherwise, it returns a NULL pointer (address 0).
Example Usage: cout << strstr(string1, string2);
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Program 10-6
// This program uses the strstr function to search an array
// of strings for a name.
#include <iostream.h>
#include <string.h> // For strstr
void main(void)
{
char prods[5][27] = {"TV327 31 inch Television",
"CD257 CD Player",
"TA677 Answering Machine",
"CS109 Car Stereo",
"PC955 Personal Computer"};
char lookUp[27], *strPtr = NULL;
int index;
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Program continues
cout << "\tProduct Database\n\n";
cout << "Enter a product number to search for: ";
cin.getline(lookUp, 27);
for (index = 0; index < 5; index++)
{
strPtr = strstr(prods[index], lookUp);
if (strPtr != NULL)
break;
}
if (strPtr == NULL)
cout << "No matching product was found.\n";
else
cout << prods[index] << endl;
}
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Starting Out with C++, 3rd Edition
Program Output With Example input
Product Database
Enter a product to search for: CD257 [Enter]
CD257 CD Player
Program Output With Example input
Product Database
Enter a product to search for: CS [Enter]
CS109 Car Stereo
Program Output With Other Example input
Product Database
Enter a product to search for: AB [Enter]
No matching product was found.
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Starting Out with C++, 3rd Edition
10.5 String/Numeric Conversion
Functions
• The C++ library provides functions for
converting a C-string representation of a
number to a numeric data type, and viceversa.
• The functions in this section require the
stdlib.h file to be included.
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Table 10-4
Function
Description
atoi
Accepts a C-string as an argument. The
function converts the C-string to an integer
and returns that value.
Example Usage: Num = atoi("4569");
atol
Accepts a C-string as an argument. The
function converts the C-string to a long
integer and returns that value.
Example Usage: Lnum = atol("500000");
atof
Accepts a C-string as an argument. The
function converts the C-string to a float and
returns that value.
Example Usage: Fnum = atof("3.14159");
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Table 10-4 Continued
Function
Description
itoa
Converts an integer to a C-string. The first argument,
value, is the integer. The result will be stored at the
location pointed to by the second argument, string.
The third argument, base, is an integer. It specifies
the numbering system that the converted integer
should be expressed in. ( 8 = octal, 10 = decimal,
16 = hexadecimal, etc. )
Example Usage: itoa(value, string, base)
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Program 10-7
// This program demonstrates the strcmp and atoi functions.
#include <iostream.h>
#include <string.h> // For strcmp
#include <stdlib.h> // For atoi
void main(void)
{
char input[20];
int total = 0, count = 0;
float average;
cout << "This program will average a series of numbers.\n";
cout << "Enter the first number or Q to quit: ";
cin.getline(input, 20);
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Program continues
while ((strcmp(input, "Q") != 0)&&(strcmp(input, "q") != 0))
{
total += atoi(input); // Keep a running total
count++; // Keep track of how many numbers entered
cout << "Enter the next number or Q to quit: ";
cin.getline(input, 20);
}
if (count != 0)
{
average = total / count;
cout << "Average: " << average << endl;
}
}
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Starting Out with C++, 3rd Edition
Program Output With Example input
This program will average a series of numbers.
Enter the first number or Q to quit: 74 [Enter]
Enter the next number or Q to quit: 98 [Enter]
Enter the next number or Q to quit: 23 [Enter]
Enter the next number or Q to quit: 54 [Enter]
Enter the next number or Q to quit: Q [Enter]
Average: 62
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10.6 Focus on Software Engineering:
Writing Your Own C-string-Handling
Functions
• You can design your own specialized
functions for manipulating C-strings.
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Program 10-8
// This program uses a function to copy a C-string into an array.
#include <iostream.h>
void stringCopy(char [], char []); // Function prototype
void main(void)
{
char first[30], second[30];
cout << "Enter a string with no more than 29 characters:\n";
cin.getline(first, 30);
stringCopy(first, second);
cout << "The string you entered is:\n" << second << endl;
}
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Program continues
//
//
//
//
//
Definition of the stringCopy function.
This function accepts two character arrays as
arguments. The function assumes the two arrays
contain C-strings. The contents of the second array is
copied to the first array.
void stringCopy(char string1[], char string2[])
{
int index = 0;
while (string1[index] != '\0')
{
string2[index] = string1[index];
index++;
}
string2[index] = '\0';
}
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Starting Out with C++, 3rd Edition
Program Output With Example input
Enter a string with no more than 29 characters:
Thank goodness it’s Friday! [Enter]
The string you entered is:
Thank goodness it's Friday!
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Starting Out with C++, 3rd Edition
Program 10-9
// This program uses the function nameSlice to "cut" the last
// name off of a string that contains the user's first and
// last names.
#include <iostream.h>
void nameSlice(char []);
// Function prototype
void main(void)
{
char name[41];
cout << "Enter your first and last names, separated ";
cout << "by a space:\n";
cin.getline(name, 41);
nameSlice(name);
cout << "Your first name is: " << name << endl;
}
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Starting Out with C++, 3rd Edition
Program continues
//
//
//
//
Definition of function nameSlice. This function accepts a
character array as its argument. It scans the array looking
for a space. When it finds one, it replaces it with a null
terminator.
void nameSlice(char userName[])
{
int count = 0;
while (userName[count] != ' ' && userName[count] != '\0')
count++;
if (userName[count] == ' ')
userName[count] = '\0';
}
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Starting Out with C++, 3rd Edition
Program Output With Example input
Enter your first and last names, separated by a space:
Jimmy Jones [Enter]
Your first name is: Jimmy
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Figure 10-3
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Figure 10-4
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Using Pointers to pass C-string
arguments
• Very useful
• Can assume string exists from address
pointed to by the pointer up to the ‘\0’
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Program 10-10
// This program demonstrates a function, countChars, that counts
// the number of times a specific character appears in a string.
#include <iostream.h>
// Function prototype
int countChars(char *, char);
void main(void)
{
char userString[51], letter;
cout << "Enter a string (up to 50 characters): ";
cin.getline(userString, 51);
cout << "Enter a character and I will tell you how many\n";
cout << "times it appears in the string: ";
cin >> letter;
cout << letter << " appears ";
cout << countChars(userString, letter) << " times.\n";
}
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Program continues
//
//
//
//
Definition of countChars. The parameter strPtr is a pointer
that points to a string. The parameter ch is a character that
the function searches for in the string. The function returns
the number of times the character appears in the string.
int countChars(char *strPtr, char ch)
{
int times = 0;
while (*strPtr != '\0')
{
if (*strPtr == ch)
times++;
strPtr++;
}
return times;
}
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Program Output With Example input
Enter a string (up to 50 characters):Starting Out With C++ [Enter]
Enter a character and I will tell you how many
times it appears in the string: t [Enter]
t appears 4 times.
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Starting Out with C++, 3rd Edition
The C++ string Class
• Offers “ease of programming” advantages
over the use of C-strings
• Need to #include the string header file
(Notice there is no .h extension.)
• Use the following statement after the
#include statements:
using namespace std;
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Program 10-12
// This program demonstrates the C++ string class.
#include <iostream>
#include <string> // Required for the string class
using namespace std;
void main(void)
{
string movieTitle;
string name("William Smith");
movieTitle = "Wheels of Fury";
cout << "My favorite movie is " << movieTitle << endl;
}
Program output
My favorite movie is Wheels of Fury
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Starting Out with C++, 3rd Edition
A note about the iostream header file
• The preceding program uses the
iostream header, not iostream.h.
• With some compilers, you must include the
iostream header instead of
iostream.h when using cout and cin
with string objects.
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Program 10-13: Using cin with a
string object
// This program demonstrates how cin can read a string into
// a string class object.
#include <iostream>
#include <string>
using namespace std;
void main(void)
{
string name;
cout << "What is your name? " << endl;
cin >> name;
cout << "Good morning " << name << endl;
}
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Starting Out with C++, 3rd Edition
Program Output With Example Input
What is your name? Peggy
Good morning Peggy
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Reading a line of input into a string
class object
• Use the getline function to read a line of
input, with spaces, into a string object.
Example code:
string name;
cout << “What is your name? “;
getline(cin, name);
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Comparing and Sorting string Objects
• You may use the relational operators to
compare string objects:
<
>
<=
>=
==
!=
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Program 10-14
// This program uses the == operator to compare the string entered
// by the user with the valid stereo part numbers.
#include <iostream>
#include <string>
using namespace std;
void main(void)
{
const float aprice = 249.0, bprice = 299.0;
string partNum;
cout << "The stereo part numbers are:\n";
cout << "\tBoom Box, part number S147-29A\n";
cout << "\tShelf Model, part number S147-29B\n";
cout << "Enter the part number of the stereo you\n";
cout << "wish to purchase: ";
cin >> partNum;
cout.setf(ios::fixed | ios::showpoint);
cout.precision(2);
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Program 10-14 (continued)
if (partNum == "S147-29A")
cout << "The price is $" << aprice << endl;
else if (partNum == "S147-29B")
cout << "The price is $" << bprice << endl;
else
cout << partNum << " is not a valid part number.\n";
}
Program Output
The stereo part numbers are:
Boom Box, part number S147-29A
Shelf Model, part number S147-29B
Enter the part number of the stereo you
wish to purchase: S147-29A [Enter]
The price is $249.00
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Other Ways to Declare string Objects
Declaration Example
Description
string address
Declares an empty string
object named address.
name is a string object
initialized with “Bill Smith”
person1 is initialized with a
copy of person2. person2
may be either a string object
or a char array.
string name(“Bill Smith”);
string person1(person2);
See Table 10-8 (page 589) for more examples.
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Table 10-10 Other Supported Operators
>>
Extracts characters from a stream and inserts
them into a string. Characters are copied
until a whitespace or the end of the string is
encountered.
<<
Inserts a string into a stream.
=
Assigns the string on the right to the string
object on the left.
+=
Appends a copy of the string on the right to
the string object on the left.
+
Returns a string that is the concatenation of
the two string operands.
[]
Implements array-subscript notation, as in
name[x]. A reference to the character in the x
position is returned.
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Starting Out with C++, 3rd Edition
Program 10-17
// This program demonstrates the C++ string class.
#include <iostream>
#include <string>
using namespace std;
void main(void)
{
string str1, str2, str3;
str1 = "ABC";
str2 = "DEF";
str3 = str1 + str2;
cout << str1 << endl;
cout << str2 << endl;
cout << str3 << endl;
str3 += "GHI";
cout << str3 << endl;
}
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Program Output
ABC
DEF
ABCDEF
ABCDEFGHI
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string class member functions
• Many member functions exist.
• See Table 10-10 (pages 592-594)
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