How to print all square submatrices of square matrix in C?

Question

Please, help me to find and print all square submatrices of square matrix from big to small square matrices in C programming language

I wrote code that works wrong:

int main() {
    int mtrx_size = 8;
    int mat[8][8] = {
        { 1, 2, 3, 4, 5, 6, 7, 8},
        { 9,10,11,12,13,14,15,16},
        {17,18,19,20,21,22,23,24},
        {25,26,27,28,29,30,31,32},
        {33,34,35,36,37,38,39,40},
        {41,42,43,44,45,46,47,48},
        {49,50,51,52,53,54,55,56},
        {57,58,59,60,61,62,63,64}
    };

    int i,j;
    int sub_mtrx_size;

    for(sub_mtrx_size = mtrx_size; sub_mtrx_size > 1 ; sub_mtrx_size--)
    {
        for(i = 0; i < sub_mtrx_size; i++)
        {
            for(j = 0; j < sub_mtrx_size; j++)
            {
                printf("%3d ", mat[i][j]);
            }
            printf("\n");
        }
        printf("\n");

    }
    return 0;

Here I need to find all 8x8, 7x7, 6x6, 5x5, 4x4, 3x3 and 2x2 submatrices.

This code prints only first 7x7, 6x6, ... , 2x2 matrices. But I need all submatrices — ata.niazov, Nov 08 '15 at 14:42

score 2 · Accepted Answer · answered Nov 08 '15 at 14:46

Your code was just printing a single sub-matrix for each size, positioned in the upper-left corner of the matrix. You need to add i and j offsets to get the sub-matrices at all positions:

#include <stdio.h>

int main() {
    int mtrx_size = 8;
    int mat[8][8] = {
        { 1, 2, 3, 4, 5, 6, 7, 8},
        { 9,10,11,12,13,14,15,16},
        {17,18,19,20,21,22,23,24},
        {25,26,27,28,29,30,31,32},
        {33,34,35,36,37,38,39,40},
        {41,42,43,44,45,46,47,48},
        {49,50,51,52,53,54,55,56},
        {57,58,59,60,61,62,63,64}
    };

    int i, j, ioff, joff, off_cnt;
    int sub_mtrx_size;

    for(sub_mtrx_size = mtrx_size; sub_mtrx_size > 1 ; sub_mtrx_size--) {
        off_cnt = mtrx_size - sub_mtrx_size + 1;
        for (ioff = 0; ioff < off_cnt; ioff++) {
            for (joff = 0; joff < off_cnt; joff++) {
                for (i = 0; i < sub_mtrx_size; i++) {
                    for (j = 0; j < sub_mtrx_size; j++) {
                        printf("%3d ", mat[i+ioff][j+joff]);
                    }
                    printf("\n");
                }
                printf("\n");
            }
        }
    }

    return 0;
}

Wow, that works, thank you. Can we do it from 2x2 to bigger? — ata.niazov, Nov 08 '15 at 14:55
You mean change the order to print the smaller first? Sure, just change the outer `sub_mtrx_size` loop to start at `2` and continue while `<= mtrx_size`, incrementing up instead of down. — Tom Karzes, Nov 08 '15 at 15:00

score 0 · Answer 2 · answered Oct 05 '16 at 19:49

Java implementation for a general nxm matrix:

private static void printSubMatrix(int[][] mat) {
    int rows=mat.length;
    int cols=mat[0].length;

    //prints all submatrix greater than or equal to 2x2
    for (int subRow = rows; subRow >= 2; subRow--) {
        int rowLimit = rows - subRow + 1;
        for (int subCol = cols; subCol >= 2; subCol--) {
            int colLimit = cols - subCol + 1;
            for (int startRow = 0; startRow < rowLimit; startRow++) {
                for (int startCol = 0; startCol < colLimit; startCol++) {

                    for (int i = 0; i < subRow; i++) {
                        for (int j = 0; j < subCol; j++) {
                            System.out.print(mat[i + startRow][j + startCol] + " ");
                        }
                        System.out.print("\n");
                    }
                    System.out.print("\n");

                }
            }
        }
    }

}

score 0 · Answer 3 · answered Jun 08 '20 at 19:23

#include <stdio.h>

int main() {
   int mtrx_size = 8;
 int mat[8][8] = {
    { 1, 2, 3, 4, 5, 6, 7, 8},
    { 9,10,11,12,13,14,15,16},
    {17,18,19,20,21,22,23,24},
    {25,26,27,28,29,30,31,32},
    {33,34,35,36,37,38,39,40},
    {41,42,43,44,45,46,47,48},
    {49,50,51,52,53,54,55,56},
    {57,58,59,60,61,62,63,64}
};

int i, j, ioff, joff, off_cnt;
int sub_mtrx_size;
/* if we make terminating condition sub_mtrx_size>=1 then we will have all 
possible square sub matrices */
for(sub_mtrx_size = mtrx_size; sub_mtrx_size >= 1 ; sub_mtrx_size--) {
    off_cnt = mtrx_size - sub_mtrx_size + 1;
    for (ioff = 0; ioff < off_cnt; ioff++) {
        for (joff = 0; joff < off_cnt; joff++) {
            for (i = 0; i < sub_mtrx_size; i++) {
                for (j = 0; j < sub_mtrx_size; j++) {
                    printf("%3d ", mat[i+ioff][j+joff]);
                }
                printf("\n");
            }
            printf("\n");
        }
    }
}

return 0;
}

Thank you for this code snippet, which might provide some limited, immediate help. A [proper explanation](https://meta.stackexchange.com/q/114762/349538) would greatly improve its long-term value by showing why this is a good solution to the problem and would make it more useful to future readers with other, similar questions. Please [edit] your answer to add some explanation, including the assumptions you’ve made. — Ardent Coder, Jun 09 '20 at 02:21

How to print all square submatrices of square matrix in C?

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