Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 7 ■ Functions
A sample run of this program is shown here:
Enter a positive whole number: 4
4! = 24
We now consider the problem of writing a function (which we will call factorial) that, given
an integer n, calculates and returns the value of n!. Since n! is an integer, the “return type” of the
function is int.
We first write the function header. It is
int factorial(int n)
It is interesting to note that the function header is all the information we need in order to use
the function correctly. Ignoring for the moment what the rest of factorial might look like, we can
use it like this:
printf("5! = %d\n", factorial(5));
or like this:
scanf("%d", &num);
printf("%d! = %d\n", num,factorial(num));
4! = 24
In the latter case, if num is 4, printf prints:
The call factorial(num) returns the value 24 directly to the printf statement.
Following the logic of Program P7.6, we write the function factorial as follows:
int factorial(int n) {
int nfac = 1;
for (int h = 2; h <= n; h++)
nfac = nfac * h;
return nfac;
} //end factorial
It is worthwhile comparing Program P7.6 and the function:
• The program prompts for and reads a value for n; the function gets a value
for n when the function is called, as in factorial(4). It is wrong to attempt
to read a value for n in this function.
• In addition to n, both the program and the function need the variables nfac
and h to express their logic.
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