Programming in C

50 Chapter 5 Program Looping

Because addition by 1 is such a common operation in programs, a special operator was

created solely for this purpose.Therefore, the expression ++nis equivalent to the expres-

sion n = n + 1. Although it might appear that n = n + 1is more readable, you will

soon become familiar with the function of this operator and will even learn to appreci-

ate its succinctness.

Of course, no programming language that offered an increment operator to add 1

would be complete without a corresponding operator to subtract 1.The name of this

operator is the decrement operatorand is symbolized by the double minus sign. So, an

expression in C that reads

bean_counter = bean_counter - 1

can be equivalently expressed using the decrement operator as

--bean_counter

Some programmers prefer to put the ++or --after the variable name, as in n++or

bean_counter--.This is acceptable, and is a matter of personal preference.

Aligning Output

One slightly disturbing thing that you might have noticed in Program 5.3’s output is the

fact that the 10th triangular number does not quite line up under the previous triangular

numbers.This is because the number 10 takes up two print positions, whereas the previ-

ous values of n,1 through 9, took up only one print position.Therefore, the value 55 is

effectively “pushed over” one extra position in the display.This minor annoyance can be

corrected if you substitute the following printfstatement in place of the corresponding

statement from Program 5.3.

printf ("%2i %i\n", n, triangularNumber);

To ver ify that this change does the trick, here is the output from the modified program

(we’ll call it Program 5.3A).

Program 5.3A Output

TABLE OF TRIANGULAR NUMBERS

n Sum from 1 to n

--- ---------------

1 1

2 3

3 6

4 10

5 15

6 21

7 28

8 36

9 45

10 55