The while statement

The while statement is similar to those used in other languages although more can be done with the expression statement - a standard feature of C.

The while has the form:

For example:

...outputs:

...to the screen.

Because the while loop can accept expressions, not just conditions, the following are all legal:-

Using this type of expression, only when the result of x, x=x+1, or x, evaluates to 0 will the while condition fail and the loop be exited.

We can go further still and perform complete operations within the while expression:

The first example counts i up to 10.

The second example uses C standard library functions (See Appendix ) getchar() - reads a character from the keyboard - and putchar() - writes a given char to screen. The while loop will proceed to read from the keyboard and echo characters to the screen until a 'q' character is read. NOTE: This type of operation is used a lot in C and not just with character reading!! (See Exercises).