CS161 Introduction to Computer Science Character Data

How do I read in Characters? Until now, we have read in character data using the following format: char ch; cin >> ch; This skips leading whitespace, –reads in 1 character and stores that character in variable ch

How do I read in Characters? An alternate form of reading in characters come in the form of the cin.get function: char ch;ch = cin.get(); //or cin.get(ch); this reads in the next character from the input buffer, even if that next character is whitespace!

How do I read in Characters? There are two different versions of the get function that read single characters. We can supply no arguments to this function and receive the next character in the input stream as the returned value. Or, we can supply a single character argument and receive the next character in the input stream through the argument (via call by reference).

How do I read in Characters? The advantage of using either of these functions is that we are able to read and store whitespace characters. If the next character in the input stream is a space, the character received will be a ' '. If the next character in the input stream is a newline, the character received will be a '\n', etc. Therefore, we can read and echo a single line of text exactly as the user types it in.

How do I read in Characters? The following two loops are equivalent and demonstrate the differences that we must adjust for when using these two versions of the get function: while ((ch = cin.get()) != '\n') cout << ch; while (cin.get(ch) && ch != '\n') //accomplishes the same cout << ch;

How do I read in Characters? For the most part, it is purely style which version of the get function we use. However, there are times when one version is more efficient than the other. For example, when no argument is supplied, the character read is the residual value and therefore can be used within a greater expression.

How do I read in Characters? This version works efficiently when we want to loop, flushing the input buffer until a newline is encountered: //flush buffer until newline while (cin.get() != '\n'); This is handy when there is a possibility of the user entering more characters than are expected It reads and "throws out" all additional characters up until (and including) the newline.

How do I read in Characters? On the other hand, the one argument version of the get function is useful when we want to detect whether or not the input operation has been successful or not. It returns a success or fail indication. It returns a non-zero value (i.e., an object of class istream) if the character is read correctly and a zero if the input operation fails or an end of file occurs.

How do I read in Characters? The following loop demonstrates this by reading characters (and echoing them) until end of file. char ch; //read until end of file (input fails) while (cin.get(ch)) cout <<ch;

Operations on Character Data With external libraries we can peform a number of operations on character data We can determine if a character is alphabetic, punctuation, a digit, upper case, or lower case using the ctype.h library All of the functions in the ctype.h library use call by value, which means none of the arguments can be modified by the functions

Operations on Character Data The ctype.h functions most useful are: isalpha(ch) which returns true (non-zero) if the value is either an upper or lowercase character and false (zero) otherwise. isdigit(ch) which returns true if the character represents one of the digits between 0-9 and false otherwise. ispunct(ch) which returns true if the character is any printable character, except a space, digit, or alphabetic and false otherwise. islower(ch) which returns true if the character is a lower case alphabetic character and false otherwise. isupper(ch) which returns true if the character is an upper case alphabetic character and false otherwise. Plus many more!

Operations on Character Data The ctype.h functions also include those we learned about earlier this term: tolower and toupper. It is important to realize that these functions are also pass by value –Which means it is impossible for tolower and toupper to modify the value of the argument; the character you send in as an argument remains unchanged Therefore, when using tolower and toupper, you must either –Use them directly in a logical expression as we learned earlier, or –Save the results in a variable: char result, ch; result = tolower(ch);