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

Chapter 7 ■ Functions
The logic for finding the HCF is the same as that used in program P5.2. The difference here is
that values for m and n will be passed to the function when it is called. In P5.2, we prompted the
user to enter values for m and n and fetched them using scanf.
Suppose the function is called with hcf(42, 24). The following occurs:
• Each of the arguments is copied to a temporary memory location.
These locations are passed to the function hcf where 42 is labeled with m,
the first parameter, and 24 is labeled with n, the second parameter. We can
picture this as:
m 42 n 24
• The while loop is executed, working out the HCF. On exit from the loop,
the HCF is stored in m, which will contain 6 at this time. This is the value
returned by the function to the place from where it was called.
• Just before the function returns, the locations containing the arguments are
thrown away; control then returns to the place from where the call was made.
Program P7.5 tests the function by reading pairs of numbers and printing the HCF of each
pair. The call to hcf is made in the printf statement. The program stops if either number is less
than or equal to 0.
Program P7.5
#include <stdio.h>
int main() {
int a, b;
int hcf(int, int);
printf("Enter two positive numbers: ");
scanf("%d %d", &a, &b);
while (a > 0 && b > 0) {
printf("The HCF is %d\n", hcf(a, b));
printf("Enter two positive numbers: ");
scanf("%d %d", &a, &b);
}
} //end main
//returns the hcf of m and n
int hcf(int m, int n) {
while (n != 0) {
int r = m % n;
m = n;
n = r;
}
return m;
} //end hcf
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