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.

Answer 1

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;
}

Answer 2

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");

                }
            }
        }
    }

}