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

Chapter 7 ■ Functions
essentially the same code as Program P7.3. Also, printDay does not return a value so its “return
type” is void.
void printDay(int d) {
if (d == 1) printf("Sunday\n");
else if (d == 2) printf("Monday\n");
else if (d == 3) printf("Tuesday\n");
else if (d == 4) printf("Wednesday\n");
else if (d == 5) printf("Thursday\n");
else if (d == 6) printf("Friday\n");
else if (d == 7) printf("Saturday\n");
else printf(“Invalid day\n”);
}
■■Tip
When we write the function, we can use any variable name we want for the parameter. We never have
to worry about how the function will be called. Many beginners mistakenly believe that if the function is called
with printDay(n), the parameter in the header must be n. But that cannot be true since it could be called
with printDay(4) or printDay(n) or printDay(j) or even printDay(n + 1). The choice is up to the
calling function.
All we need to know is that whatever the value of the argument, that value will be assigned
to d (or whatever variable we happen to use as the parameter), and the function will be executed
assuming the parameter (d, in our case) has that value.
We now rewrite Program P7.3 as P7.4 to illustrate how the function fits into an overall
program and how it can be used.
Program P7.4
#include <stdio.h>
int main() {
int n;
void printDay(int);
printf("Enter a day from 1 to 7: ");
scanf("%d", &n);
printDay(n);
} //end main
void printDay(int d) {
if (d == 1) printf("Sunday\n");
else if (d == 2) printf("Monday\n");
else if (d == 3) printf("Tuesday\n");
else if (d == 4) printf("Wednesday\n");
else if (d == 5) printf("Thursday\n");
else if (d == 6) printf("Friday\n");
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