Thread: array asking for constant value (I am giving constant values)

My task is to create a matrix of random numbers of nxn size. However, there is an error I can´t solve, it is telling me that the expression needs to have a constant value (on the variable "matrix" in the for loop). What am I doing wrong?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>




int main()
{
    srand(NULL);


     int rows;
     int columns;
    
    printf("define the size of the matrix\n number of rows\n");
    scanf_s("%d", &rows);
    printf("number of columns\n");
    scanf_s("%d", &columns);
    const int x=rows;
    const int y=columns;
    


    for (int i = 1; i < x; ++i)
    {
        for (int j = 1; j <y; ++j)
        {
            int matrix[x][y] = rand() % 21 + (-10);
            printf("%d     ", matrix[i][j]);
        }
        printf("\n");
    }
}

You have quite a few errors.
The srand call should be:

Code:

srand(time(NULL));

x and y seem useless. You already have rows and columns so just use those.

You need to define the matrix before the loop.

Code:

int matrix[rows][columns];    // assuming C99

Your loops need to start at 0 not 1 since array indices start at 0.

You need to index the matrix with i and j.

Instead of + (-10) why not just - 10 ?

Thanks for your answer. I have corrected the mistakes I made. However, the declaration of the matrix before the loop is asking me for constant values again, how could I solve this problem, because whenever I declare rows and columns variables with const int, it requires me an initializer.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>




int main()
{
    srand(time(NULL));


    const int rows;
     int columns;
    
    printf("define the size of the matrix\n number of rows\n");
    scanf_s("%d", &rows);
    printf("number of columns\n");
    scanf_s("%d", &columns);
    int matrix[rows][columns];
    


    for (int i = 0; i < rows; ++i)
    {
        for (int j = 0; j <columns; ++j)
        {
          matrix[i][j] = rand() % 21 -10;
            printf("%d     ", matrix[i][j]);
        }
        printf("\n");
    }
}