Characters and Strings in C

Readings

Please read the following materials carefully:

• King, Sections 13.1-13.6, pages 277-300.

References

This lab assumes that you have access to a C programming language reference, particularly for the C string function library. If you do not have a published reference in paper form, you might consider the following on-line reference:

• Eric Huss, The C Library Reference, 1997. (See particularly section 2.14.)

Additional Notes

Reading Character Data

C provides two equivalent approaches for reading individual characters.

• The C function getchar() reads and returns a single character.
  Example:

   
     char ch;
     ch = getchar();
  

• The c format for scanf reads an individual character.
  Example:

   
     char ch;
     scanf ("%c", &ch);
  

When reading character data with either getchar or %c with scanf, the first character is read and recorded; that is, the process of reading a character does NOT skip over white space.

Reading Strings

C also provides at least three approaches for reading strings of characters. Each function has its own special characteristics.

• The s format for scanf reads a sequence of non-white-space characters. As with all strings, a null character ('\0') is added at the end of the string.
  Example:

   
     char str[10];      /* allow room for 10 characters, including the null */
     scanf ("%s", str); /* since str is an array, the variable represents a
                           base address and no ampersand & is added */
  

• The C function gets() reads an entire line or until end of file. As with scanf, a null character is added at the end of the string.
  Example:

   
     char str[10];
     gets (str);     
  

• The C function fgets() reads up to n characters from a line or until end of file, . As with scanf, a null character is added at the end of the string.
  Example:

   
     char str[10];             /* stdin is the C variable for "standard input" */
     fgets (str, 10, stdin);   /* up to 9 characters are read from the
                                  terminal, leaving room for a null character
                                  at the end */
                             
  

As with reading character data , stored input starts immediately with the first character read; the process of reading a string does NOT skip over white space.

Warning: Both scanf and gets read characters (until white space or the end of a line), without regard for the size of the string array. If more characters are read than fit in the array, the characters may overflow to fill data stored in other variables. Thus, only fgets can be considered "safe".

Characters as Integers

The following example shows that char is considered to be a type of integer, and integer arithmetic may be performed on their values.

    #include <stdio.h>

    int main() {
       char ch;
       for (ch = 'A'; ch < 127; ch++) {
         printf("Character: %c", ch);
         printf("\t ASCII: %d \n", ch);
       }

       return 0;
    }

The following example illustrates that some characters represent actions rather than just printing a symbol.

    #include <stdio.h>

    int main() {
        char ringBell = '\a';
        char tab = '\t';
        char backspace = '\b';
        char ch;
        
        printf("Now hit the Enter key. \n");
        ch = getchar();   /* wait for the user to enter something */
        printf("Beep %c \n", ringBell);
        
        printf("Now hit the Enter key. \n");
        ch = getchar();   /* wait for the user to enter something */
        printf("These %c words %c have %c tabs %c between %c them.\n",
               tab, tab, tab, tab, tab);
        
        printf("Now hit the Enter key. \n");
        ch = getchar();   /* wait for the user to enter something */
        printf("Can you read the word: hockey? %c%c%c%c%c%c%c%c         \n",
               backspace, backspace, backspace, backspace, 
               backspace, backspace, backspace, backspace );
    
        return 0;
    }

This document is available on the World Wide Web as

http://www.cs.grinnell.edu/~walker/courses/161.sp10/readings/reading-strings-c.shtml

created 10 April 2008 last revised 6 March 2010
For more information, please contact Henry M. Walker at walker@cs.grinnell.edu.