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assignment-s-19.c

Problem Statement

Write a program to calculate the GCD of two numbers (i) using recursion (ii) without recursion

Metadata

Property Detail
Author Amit Dutta amitdutta4255@gmail.com
Date 22 Dec 2025
License MIT License (See the LICENSE file for details)
Difficulty Beginner (index: 2 / 10)

Concepts

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  • Recursion
  • Iteration

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Source Code

#include <stdio.h>

int gcd_tail_rec(int, int);
int gcd_rec(int, int);
int gcd_ite(int, int);

int main()
{
    int a, b;
    printf("Enter two number: ");
    scanf("%d %d", &a, &b);
    if (a < 0)
        a = -a;
    if (b < 0)
        b = -b;
    printf("\nGCD (Tail-Recursion) of %d and %d is = %d", a, b, gcd_tail_rec(a, b));
    printf("\nGCD (Recursion) of %d and %d is      = %d", a, b, gcd_rec(a, b));
    printf("\nGCD (Iteration) of %d and %d is      = %d", a, b, gcd_ite(a, b));
    return 0;
}

int gcd_tail_rec(int a, int b)
{
    if (b == 0)
    {
        return a;
    }
    else
    {
        return gcd_tail_rec(b, a % b);
    }
}

int gcd_rec(int a, int b)
{
    if (b == 0)
    {
        return a;
    }
    else
    {
        return gcd_rec(b, a % b);
    }
}

int gcd_ite(int a, int b)
{
    int temp;
    while (b > 0)
    {
        temp = b;
        b = a % b;
        a = temp;
    }
    return a;
}

Explanation

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    You are explaining a C programming code to a beginner.

    STRICT RULES:

    - Only use the given code. Do NOT assume anything not present.

    - Do NOT add extra examples.

    - Keep explanation clear and short.

    - If something is unclear, say "Not clear from code".

    - Follow the exact format below. Do NOT change headings.

    FORMAT:

    [START]

    ## What it does

    (Explain the overall purpose in 1-2 sentences)

    ## Step-by-step

    (Explain how the code works in steps, simple language)

    ## Key Concepts

    (List concepts like loop, condition, function, etc.)

    ## Notes

    (Mention any limitations, errors, or assumptions)

    [END]

    CODE (assignment-s-19.c):

    #include <stdio.h>

    int gcd_tail_rec(int, int);
    int gcd_rec(int, int);
    int gcd_ite(int, int);

    int main()
    {
        int a, b;
        printf("Enter two number: ");
        scanf("%d %d", &a, &b);
        if (a < 0)
            a = -a;
        if (b < 0)
            b = -b;
        printf("\nGCD (Tail-Recursion) of %d and %d is = %d", a, b, gcd_tail_rec(a, b));
        printf("\nGCD (Recursion) of %d and %d is      = %d", a, b, gcd_rec(a, b));
        printf("\nGCD (Iteration) of %d and %d is      = %d", a, b, gcd_ite(a, b));
        return 0;
    }

    int gcd_tail_rec(int a, int b)
    {
        if (b == 0)
        {
            return a;
        }
        else
        {
            return gcd_tail_rec(b, a % b);
        }
    }

    int gcd_rec(int a, int b)
    {
        if (b == 0)
        {
            return a;
        }
        else
        {
            return gcd_rec(b, a % b);
        }
    }

    int gcd_ite(int a, int b)
    {
        int temp;
        while (b > 0)
        {
            temp = b;
            b = a % b;
            a = temp;
        }
        return a;
    }