Lost with getting random numbers into my matrix in c

Question

#include <stdio.h>
#include <stdlib.h> 
#include <time.h>
#define COL 20
#define ROW 20
void PopulateArray2DUnique(int [][COL],  int, int , int , int );
void DisplayArray2D(int [][COL], int, int );


int main()
{
    int matrix[ROW][COL], r ,c ,i , j;
    int max = 400;
    int min = 0;


    printf("Enter the amount of rows and cols you would like\n Must be under 20!\n");
    scanf("%d%d\n",&r,&c);

    PopulateArray2DUnique(matrix,r,c,min,max);
    DisplayArray2D(matrix,r,c);



    return 0;
}

void PopulateArray2DUnique(int matrix[][COL], int r,int c, int min, int max)
{


  int i, j;



    srand(time(NULL));
    for(i = 0; i<r; i++)
    {
         for(j = 0; j<c; j++)
     {
            matrix[i][j] = rand() % (max + min)+min;
     }
    }

}

void DisplayArray2D(int matrix[][COL], int r,int c)
{
    int i,j;
    for(i = 0; i < r; i++)
{
    for(j = 0; j < c; j++)
    {
        printf("%4d ", matrix[i][j]);
    }
    printf("\n");
}


}

what this program does (so far) is ask user to input the size of the matrix, then the function PopulateArray2DUnique generates random values for the matrix!

asks me to input the size of rows and cols twice

Answer 1

The following code will allow the user to enter the matrix dimensions separated by a space, as in 2 2 for a 2-by-2 matrix, and then print the contents of the matrix with random numbers in the range from min to max:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define COL 20
#define ROW 20
//void PopulateArray2DUnique(int [][COL], unsigned int,unsigned int , int , int );

int main()
{
    int matrix[ROW][COL], r ,c ,i , j;
    int max = 100;
    int min = 0;
    int rand_num;
    float fraction;

    printf("Enter the amount of rows and cols you would like\n Must be under 20!\n");
    scanf("%d %d",&r,&c);

    if ((r > ROW) || (r < 1)) {
        r = ROW;
    }
    if ((c > COL) || (c < 1)) {
        c = COL;
    }
    for (i=0;i<r;i++){
        for(j=0;j<c;j++){
            rand_num = rand();
            fraction = ((float) rand_num / (float) RAND_MAX);
            matrix[i][j] = (int) (min + (fraction * max));
        }
    }

    for (i=0;i<r;i++){
        for(j=0;j<c;j++){
        printf("The value for ROW: %d, COLUMN %d IS: %d\n", i, j, matrix[i][j]);
        }
    }
    //PopulateArray2DUnique(matrix,rowsize,colsize,min,max);
    return 0;
}

The output is as follows:

$ ./a.out
Enter the amount of rows and cols you would like
 Must be under 20!
2 2
The value for ROW: 0, COLUMN 0 IS: 84
The value for ROW: 0, COLUMN 1 IS: 39
The value for ROW: 1, COLUMN 0 IS: 78
The value for ROW: 1, COLUMN 1 IS: 79

Answer 2

If your issue is simply creating random integers to plug into the matrix then use the random function with srand and time as explained here

Answer 3

srand(time(NULL));

for(i = 0; i < rowsize; i++)
{
    for(j = 0; j < colsize; j++)
    {
        matrix[i][j] = (rand() % (max-min)) + min;
    }
}

Given rand() % N will produce numbers from 0 to N-1, so instead of using max we can use (max+1) to make it inclusive, we need to produce numbers from min to max, first we subtract by min to get numbers from min-min to max-min, this will produce numbers from 0 to max-min, then add min to the result, to get a range from min to max

(rand() % ((max+1)-min)) + min

Then finally to print the matrix in a tabular way

for(i = 0; i < rowsize; i++)
{
    for(j = 0; j < colsize; j++)
    {
        printf("%4d ", matrix[i][j]);
    }
    printf("\n");
}

Reading the input from user should be like this, keep asking until a valid input

r=20;
while (r <= 0 || r >= 20)
{
    printf("Enter how many rows (under 20) then press Enter: ");
    scanf("%d", &r);
}

c=20;
while (c <= 0 || c >= 20)
{
    printf("Enter how many columns (under 20) then press Enter: ");
    scanf("%d", &c);
}