Chapter 10 – Characters, Strings, and the string Class

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Starting Out with C++, 3rd Edition

Chapter 10 – Characters, Strings, and the string Class

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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 10-1CharacterMacro

Description

is a lp h a Returns true (a nonzero number) if the argument is a letter of the alphabet.Returns 0 if the argument is not a letter.

is a ln u m Returns true (a nonzero number) if the argument is a letter of the alphabet or adigit. Otherwise it returns 0.

isd ig it Returns true (a nonzero number) if the argument is a digit 0–9. Otherwise itreturns 0.

is lo w e r Returns true (a nonzero number) if the argument is a lowercase letter.Otherwise, it returns 0.

isp r in t Returns true (a nonzero number) if the argument is a printable character(including a space). Returns 0 otherwise.

isp u n c t Returns true (a nonzero number) if the argument is a printable character otherthan a digit, letter, or space. Returns 0 otherwise.

isu p p e r Returns true (a nonzero number) if the argument is an uppercase letter.Otherwise, it returns 0.

is sp a c e 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 inputEnter any character: A [Enter]The character you entered is: AIts ASCII code is: 65That's an alphabetic character.The letter you entered is uppercase.Program Output With Other Example inputEnter any character: 7 [Enter]The character you entered is: 7Its ASCII code is: 55That'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 prototypebool 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 continuesif (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 lettersfor (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 digitsfor (int count = 3; count < 7; count++){

if (!isdigit(custNum[count]))return false;

}return true;

}

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Program Output With Example inputEnter 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 inputEnter 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

to u p p e r Returns the uppercase equivalent of its argument.

to lo w e r 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 inputThis program calculates the area of a circle.Enter the circle's radius: 10 [Enter]The area is 314.16Calculate another? (Y or N) b Enter]Calculate another? (Y or N) y [Enter]Enter the circle's radius: 1 [Enter]The area is 3.14Calculate 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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Program Output with Example inputEnter 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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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 10-3Function Description s trlen 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); s trc a t 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);

s trc p y 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);

s trn c p y 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);

s trc m p 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))

s trs tr 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 continuescout << "\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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Program Output With Example inputProduct Database

Enter a product to search for: CD257 [Enter]CD257 CD PlayerProgram Output With Example inputProduct Database

Enter a product to search for: CS [Enter]CS109 Car StereoProgram Output With Other Example inputProduct DatabaseEnter a product to search for: AB [Enter]No matching product was found.

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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 vice-versa.

• The functions in this section require the stdlib.h file to be included.

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Table 10-4Function 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 totalcount++; // Keep track of how many numbers enteredcout << "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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Program Output With Example inputThis 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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Program Output With Example inputEnter 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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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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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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Program Output With Example inputEnter 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 prototypeint 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 inputEnter a string (up to 50 characters):Starting Out With

C++ [Enter]Enter a character and I will tell you how manytimes it appears in the string: t [Enter]t appears 4 times.

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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 classusing namespace std;

void main(void){

string movieTitle;string name("William Smith");

movieTitle = "Wheels of Fury";cout << "My favorite movie is " << movieTitle << endl;

}

Program outputMy favorite movie is Wheels of Fury

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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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Program Output With Example InputWhat is your name? PeggyGood 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;

elsecout << partNum << " is not a valid part number.\n";

}

Program OutputThe stereo part numbers are: Boom Box, part number S147-29A Shelf Model, part number S147-29BEnter the part number of the stereo youwish 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.

string name(“Bill Smith”); name is a string object initialized with “Bill Smith”

string person1(person2); person1 is initialized with a copy of person2. person2 may be either a string object or a char array.

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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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

ABCDEFABCDEFABCDEFGHI

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string class member functions

• Many member functions exist.• See Table 10-10 (pages 592-594)

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Chapter 10 – Characters, Strings, and the string Class