Programming Tutorials

Character Counting sample program in C

By: Grenfel in C Tutorials on 2007-09-20  

The following C program counts characters; it is similar to the copy program.

   #include <stdio.h>

   /* count characters in input; 1st version */
   main()
   {
       long nc;

       nc = 0;
       while (getchar() != EOF)
           ++nc;
       printf("%ld\n", nc);
   }

The statement

   ++nc;

presents a new operator, ++, which means increment by one. You could instead write nc = nc + 1 but ++nc is more concise and often more efficient. There is a corresponding operator -- to decrement by 1. The operators ++ and -- can be either prefix operators (++nc) or postfix operators (nc++); these two forms have different values in expressions, but ++nc and nc++ both increment nc. For the moment we will will stick to the prefix form.

The character counting program accumulates its count in a long variable instead of an int. long integers are at least 32 bits. Although on some machines, int and long are the same size, on others an int is 16 bits, with a maximum value of 32767, and it would take relatively little input to overflow an int counter. The conversion specification %ld tells printf that the corresponding argument is a long integer.

It may be possible to cope with even bigger numbers by using a double (double precision float). We will also use a for statement instead of a while, to illustrate another way to write the loop.

    #include <stdio.h>

   /* count characters in input; 2nd version */
   main()
   {
       double nc;

       for (nc = 0; gechar() != EOF; ++nc)
           ;
       printf("%.0f\n", nc);
   }

printf uses %f for both float and double; %.0f suppresses the printing of the decimal point and the fraction part, which is zero.

The body of this for loop is empty, because all the work is done in the test and increment parts. But the grammatical rules of C require that a for statement have a body. The isolated semicolon, called a null statement, is there to satisfy that requirement. We put it on a separate line to make it visible.

Before we leave the character counting program, observe that if the input contains no characters, the while or for test fails on the very first call to getchar, and the program produces zero, the right answer. This is important. One of the nice things about while and for is that they test at the top of the loop, before proceeding with the body. If there is nothing to do, nothing is done, even if that means never going through the loop body. Programs should act intelligently when given zero-length input. The while and for statements help ensure that programs do reasonable things with boundary conditions.