Chapter 10 – Characters, Strings, and the string Class 1 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 2 Starting Out with C++, 3rd Edition 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: 3 Starting Out with C++, 3rd Edition 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; 4 Starting Out with C++, 3rd Edition 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"; } 5 Starting Out with C++, 3rd Edition 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. 6 Starting Out with C++, 3rd Edition 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); 7 Starting Out with C++, 3rd Edition 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++) { 8 Starting Out with C++, 3rd Edition 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; } 9 Starting Out with C++, 3rd Edition 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 10 Starting Out with C++, 3rd Edition 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 11 Starting Out with C++, 3rd Edition Table 10-2 Function Description toupper Returns the uppercase equivalent of its argument. tolower Returns the lowercase equivalent of its argument. 12 Starting Out with C++, 3rd Edition 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); 13 Starting Out with C++, 3rd Edition 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'); } 14 Starting Out with C++, 3rd Edition 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] 15 Starting Out with C++, 3rd Edition 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 16 Starting Out with C++, 3rd Edition 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'); } 17 Starting Out with C++, 3rd Edition 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++; } } 18 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! 19 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 20 Starting Out with C++, 3rd Edition Figure 10-2 21 Starting Out with C++, 3rd Edition 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); 22 Starting Out with C++, 3rd Edition 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; 23 Starting Out with C++, 3rd Edition 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; } 24 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. 25 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. 26 Starting Out with C++, 3rd Edition 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"); 27 Starting Out with C++, 3rd Edition 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) 28 Starting Out with C++, 3rd Edition 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); 29 Starting Out with C++, 3rd Edition 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; } } 30 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 31 Starting Out with C++, 3rd Edition 10.6 Focus on Software Engineering: Writing Your Own C-string-Handling Functions • You can design your own specialized functions for manipulating C-strings. 32 Starting Out with C++, 3rd Edition 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; } 33 Starting Out with C++, 3rd Edition 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'; } 34 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! 35 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; } 36 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'; } 37 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 38 Starting Out with C++, 3rd Edition Figure 10-3 39 Starting Out with C++, 3rd Edition Figure 10-4 40 Starting Out with C++, 3rd Edition Using Pointers to pass C-string arguments • Very useful • Can assume string exists from address pointed to by the pointer up to the ‘\0’ 41 Starting Out with C++, 3rd Edition 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"; } 42 Starting Out with C++, 3rd Edition 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; } 43 Starting Out with C++, 3rd Edition 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. 44 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; 45 Starting Out with C++, 3rd Edition 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 46 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. 47 Starting Out with C++, 3rd Edition 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; } 48 Starting Out with C++, 3rd Edition Program Output With Example Input What is your name? Peggy Good morning Peggy 49 Starting Out with C++, 3rd Edition 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); 50 Starting Out with C++, 3rd Edition Comparing and Sorting string Objects • You may use the relational operators to compare string objects: < > <= >= == != 51 Starting Out with C++, 3rd Edition 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); 52 Starting Out with C++, 3rd Edition 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 53 Starting Out with C++, 3rd Edition 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. 54 Starting Out with C++, 3rd Edition 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. 55 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; } 56 Starting Out with C++, 3rd Edition Program Output ABC DEF ABCDEF ABCDEFGHI 57 Starting Out with C++, 3rd Edition string class member functions • Many member functions exist. • See Table 10-10 (pages 592-594) 58 Starting Out with C++, 3rd Edition