# Functions Exercises

Write a C program to find LCM of two numbers using recursion. How to find LCM of two numbers in C programming using recursion. Logic to find LCM of two numbers using recursion.

**Required knowledge**

Basic C programming, If else,for loop,Functions, Recursion

**Logic to find LCM of two numbers using recursion**

Finding LCM using iterative method involves three basic steps:

- Initialize multiple variable with the maximum value among two given numbers.
- Check whether multiple clearly divides both number or not. If it does, then end the process and return multiple as LCM.
- If multiple doesn't divides both given numbers then increment multiple by the max values among both given numbers.

Repeat steps 2 to 3 till you find LCM. To convert the above iterative approach of finding LCM into recursive we will use step 2 as our base condition.

**Program to find LCM using recursion**

/** * C program to find LCM of two numbers using recursion */ #include <stdio.h> /* Function declaration */ int lcm(int a, int b); int main() { int num1, num2, LCM; /* Input two numbers from user */ printf("Enter any two numbers to find lcm: "); scanf("%d%d", &num1, &num2); /* * Ensures that first parameter of LCM function * is always less than second */ if(num1 > num2) LCM = lcm(num2, num1); else LCM = lcm(num1, num2); printf("LCM of %d and %d = %d", num1, num2, LCM); return 0; } /** * Recursive function to find lcm of two numbers 'a' and 'b'. * Here 'a' needs to be always less than 'b'. */ int lcm(int a, int b) { static int multiple = 0; /* Increments multiple by adding max value to it */ multiple += b; /* * Base condition of recursion * If found a common multiple then return the multiple. */ if((multiple % a == 0) && (multiple % b == 0)) { return multiple; } else { return lcm(a, b); } }

Note: Since we don't want the variable multiple to re-initialize again and again by recursive function calls, therefore I have declared it as static i.e. static int multiple = 0;.

Also you can remove the other condition as it is not necessary. Means you can simply write the if statement as if(multiple % a == 0). Since the variable multiple is always a multiple of b.

**Output**

Enter any two numbers to find lcm: 12

30

LCM of 12 and 30 = 60