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

Chapter 7 ■ Functions
The following is a sample run of P7.5:
Enter two positive numbers: 42 24
The HCF is 6
Enter two positive numbers: 32 512
The HCF is 32
Enter two positive numbers: 100 31
The HCF is 1
Enter two positive numbers: 84 36
The HCF is 12
Enter two positive numbers: 0 0
We emphasize again that even though the function is written with parameters m and n, it can
be called with any two integer values – constants, variables, or expressions. In particular, it does
not have to be called with variables named m and n. In our program, we called it with a and b.
We remind you that in order to use hcf in main, we must “declare” it using the function prototype
int hcf(int, int);
If you wish, you could write the two int declarations in main as one:
int a, b, hcf(int, int);
7.6.1 Using HCF to Find LCM
A common task in arithmetic is to find the lowest common multiple (LCM) of two numbers.
For example, the LCM of 8 and 6 is 24 since 24 is the smallest number that can divide both 8
and 6 exactly.
If we know the HCF of the two numbers, we can find the LCM by multiplying the numbers
and dividing by their HCF. Given that the HCF of 8 and 6 is 2, we can find their LCM by working out
which is 24. In general,
8 ´ 6
2
LCM(m, n) = (m x n) / HCF(m, n)
Knowing this, we can easily write a function lcm which, given two arguments m and n, returns
the LCM of m and n.
//returns the lcm of m and n
int lcm(int m, int n) {
int hcf(int, int);
return (m * n) / hcf(m, n);
} //end lcm
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