[SOLVED] How to traverse a 2D array using recursion

Issue

I’m looking for someone to help me to traverse and display the 2d array or matrix using recursion.

void display(int** matrix1,int row, int column)

This is what I am doing for the 1D array:

void print_array(int arr[], int size, int i)
{

    if (i == size) {
        cout << endl;
        return;
    }
    cout << arr[i] << " ";
    print_array(arr, size, i+1);
}

I know how to traverse 1D array but unable to do this.
I want to display each element in the matrix using recursion.

Solution

I am sure that you need to write a C program or a C++ program but using functionality of C due to your declaration of “2D array” like int **.:)

The function can be easy implemented if to use one more auxiliary recursive function.

Here is a demonstrative program

#include <stdio.h>

void display_row( int *a, size_t column )
{
    column == 0 ? ( void )putchar( '\n' )
                : ( void )( printf( "%2d ", *a ), display_row ( ++a, --column ) );
}

void display( int **a, size_t row, size_t column )
{
    if ( row != 0 )
    {
        display_row( *a, column );
        display( ++a, --row, column );
    }
}

int main(void) 
{
    enum { M = 3, N = 4 };

    int a1[N] = {  1,  2,  3,  4 };
    int a2[N] = {  5,  6,  7,  8 };
    int a3[N] = {  9, 10, 11, 12 };

    int *a[M] = { a1, a2, a3 };

    display( a, M, N );

    return 0;
}

The program output is

 1  2  3  4 
 5  6  7  8 
 9 10 11 12 

If not to use an auxiliary function then another approach is to use a static variable inside the recursive function.

Here is a demonstrative program that uses a recursive function with a static variable.

#include <stdio.h>

void display( int** a, size_t row, size_t column )
{
    static size_t pos = 0;

    if ( row != 0 && column == 0 )
    {
        putchar( '\n' );
        size_t tmp = column;
        column = pos;
        pos = tmp;
        --row;
        ++a;
    }       

    if ( row )  
    {
        printf( "%2d ", a[0][pos++] );
        display( a, row, --column );
    }       
}

int main(void) 
{
    enum { M = 3, N = 4 };

    int a1[N] = {  1,  2,  3,  4 };
    int a2[N] = {  5,  6,  7,  8 };
    int a3[N] = {  9, 10, 11, 12 };

    int *a[M] = { a1, a2, a3 };

    display( a, M, N );

    return 0;
}

Its output is the same as shown above.

If you need a C++ program then just include headers

#include <iostream>
#include <iomanip>

and instead of for example this call of printf

printf( "%2d ", a[0][pos++] );

use

std::cout << std::setw( 2 ) << a[0][pos++];

Answered By – Vlad from Moscow

Answer Checked By – Jay B. (BugsFixing Admin)

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