CS 1400

Chapter 10

Strings

Character testing library

• #include <cctype>• bool isalpha (char c);• bool isalnum (char c);• bool isdigit (char c);• bool islower (char c);• bool isupper (char c);• bool ispunct (char c);• bool isprint (char c);• bool isspace (char c);

Example…• Verify that a password contains at least 5 alpha

and 3 numeric characters

char password[10];int numalpha = 0, numdigit = 0;cin >> password;for (int n=0; n<strlen(password); n++){ if (isalpha(password[n]))

numalpha++;else if (isdigit(password[n]))

numdigit++;}if (numalpha >= 5 && numdigit >= 3)

cout << “valid!\n”;

Character conversion library

• #include <cctype>• char toupper (char c);• char tolower (char c);

Example…

• Convert a C-string to all lower-case

void ConvertToLower (char line[ ]){ int len = strlen(line);

for (n=0; n<len; n++)if (isupper(line[n]))

line[n] = tolower(line[n]);}

C-String library functions

• #include <cstring>• int strlen (char str[ ]);• void strcpy (char dest[ ], char src[ ]);• int strcmp (char src1[ ], char src2[ ]);

FYI• void strcat (char dest[ ], char src[ ]);• void strncpy (char dest[ ], char src[ ], int count);• char* strstr (char str[ ], char search[ ]);

The NULL pointer…

• A special pointer value of zero has been defined as NULL. Some functions returning pointers will return NULL on some occasions

• Ex:char line[80];

cin >> line;

if (strstr (line, “Mr.”) == NULL)

cout << “this line does not contain Mr.”;

String-to-Number conversions

• #include <cstdlib>int atoi (char word[ ]);

int atol (char word[ ]);

float atof (char word[ ]);

Note: itoa() has been deprecated under Microsoft Visual Studio .NET.

Number-to-string conversions

• #include <iostream>void sprintf (char line[ ], format_literal, var_list);

// convert these variables into a C-String

– format_literal: a C-string containing a format specifier for each variable to be converted

– var_list: a comma-separated list of variables

Format Specifiers for sprintf()

• %d an integer position• %f a float position• %s a C-String position• %nd an integer position of n columns• %n.mf A float position of n columns,

rounding to m decimal places

any word that doesn’t begin with % is simply inserted as a literal…

sprintf() examples…

char line[80];int x = 1234; float y = 3.14159;sprintf (line, “age: %d cost: $ %f”, x, y);cout << line << endl;sprintf (line, “cost rounded: $ %5.2f”, y);cout << line << endl;

output age: 1234 cost: $ 3.14159 cost rounded: $ 3.14

C-String example:

• Write a program to read in a form letter containing occurrences of the word “CUSTOMER”. Next, allow the user to input a person’s name. Now, replace all occurrences of the word “CUSTOMER” with this name and print the letter.

formletter.zip

Form letter

Dear CUSTOMER:

Congratulations! You have won one of the following trips; 7 days in Hawaii, 10 days in San Francisco, or one day in Park City being hounded by a condo salesman. Yes CUSTOMER, this is the dream award of a lifetime! To claim your trip CUSTOMER, just call 1-800-CHEATEM.

We look forward to taking you on this trip,Bogus Travel and Condo Sales

Example execution:

Enter a customer name: Fred

Dear Fred:Congratulations! You have won one of the following trips; 7 days in Hawaii, 10 days in San Francisco, or one day in Park City being hounded by a condo salesman. Yes Fred, this is the dream award of a lifetime! To claim your trip Fred, just call 1-800-CHEATEM.

We look forward to taking you on this trip,Bogus Travel and Condo Sales

Manipulating strings

• There are several ways of manipulating textual strings;– C-strings

• strings are stored in arrays of characters

– C++ string objects• strings are stored in an abstract data type

– CString objects• strings are stored in an abstract data type specific

to Microsoft GUIs.

– etc…..

The C++ string class

• A class is an abstract data type -- a new programmer-defined data type with its own set of manipulation functions

• class functions are called using “dot” notation. You’ve seen this before!

ifstream fin;

fin.open(“myfile.txt”);

The C++ string class• #include <string>• A C++ string variable can be treated as a

simple variable capable of holding a string. A C++ string is not just a char array.

• A C++ string can be assigned and compared with ordinary assignment and comparison operators such as = and <.

string word1, word2;word1 = “Hello”; cin >> word2;if (word1 < word2)

cout << “less than”;

C++ string class

• How big is a string variable (how many characters can it hold)? – as big as it needs to be

• How is this all accomplished?– don’t know and don’t care (at this point)

Concatenation

• The “+” operator can be used between two strings, but it means concatenation (not addition)string word1 = “Hello “;

string word2 = “and Goodbye!”;

string line;

line = word1 + word2;

cout << line << endl;

Accessing individual characters…

• Individual characters in a string can be accessed using bracket [ ] notation.cout << word1[3]; // output character 3

word1[4] = ‘X’; // replace character 4

While this makes it appear like a string is an array, it is not! In C++, an operator used with a class means anything the designer of that class wants it to. (More on this to come…)

string member functionsstring line, word;

line.append (word); // append word onto line

cout << line.length(); // output the length of line

line.erase (position, count); // erase count characters beginning at position

pos = line.find (search, position);

// determine the index position of search in line (beginning at position)

line.swap (word); // swap the contents of line and word

cout << line.substr (position, count); // output a substring

beginning at position for count characters

and many many more…

Conversions…

• A C-string or literal can be assigned to a string

char name[5] = “Fred”;

string othername;

othername = name;

• But a string cannot be assigned to a C-string

name = othername;

Rule of Thumb…

• There are many compatibilities between C-strings and strings, but it is best to use one or the other in a program (at this point in your career).

Examples…

• Output “YES” if an input string contains the word “MONEY”

• Find and output a dollar-and-cents amount in a string.

• Erase all the blanks in a string.

• Capitalize the name “fred” in a string.

• Replace <last>,<first> with <first> <last>

Sorting stringsvoid SelectionSort (string array[ ], int size){ int smallest_position; for (int n=0; n<size-1; n++) { smallest_position = FindSmallest (array, n, size);

Swap (array, n, smallest_position); }}

If you have a sorting function that works for integer arrays, it will also work for string arrays – just change int to string!

sorting.zip

Find_Smallest()

int FindSmallest (string array[ ], int start, int size){ int position = start; string smallest = array[start]; for (int k=start+1; k<size; k++)

if (array[k] < smallest){ smallest = array[k]; position = k;}

return position;}

Swap()

void Swap (string array[ ], int j, int k){ string temp; temp = array[j]; array[j] = array[k]; array[k] = temp;}

or…void Swap (string array[ ], int j, int k){ array[j].swap(array[k]);}

Input for strings…

ifstream fin; string string_a, string_b, string_c;

char c;…fin >> string_a; // input the next word

getline (fin, string_b); // input next line

while (fin.get(c))string_c += c; // input to end of file

More string member funcs…

string s;s.insert (pos, substr); // insert substr at poss.replace(pos, n, str); // replace n chars at pos with str

example: s = “ me”;s.insert(0,”hello”);s.replace(3, 2, “p”);cout << s; // outputs “help me”

C++ string example:

• Write a program to read in a form letter containing occurrences of the word “CUSTOMER”. Next, allow the user to input a person’s name. Now, replace all occurrences of the word “CUSTOMER” with this name and print the letter.

stringformletter.zip

Example

• Write a program to prompt a user to input a value. Next, add 6% and output this result in standard commercial notation (commas and dollar sign, rounded to 2 dec. places)

Input a value: 23456789.01234

With 6% added: $24,864,196.35

strings.cpp