Fill a defined 2D Array with random numbers in C

I've created this 2D 21x21 array that has all it's values set to -1. I wrote it to print the address and value and somehow it only starts at [6][19] why?

What i want to do is to replace some of the -1 values with random numbers from 0 to 100 in the same array. I know i need to seed it with srand but i'm having problems connecting the functions since i'm a total beginner in C.

The 2D array is:

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



int main()
{
int a[21][21], i , j;

for (i = 0; i < 21; i++)
{
    for ( j = 0; j < 21; j++)
    {
        a[i][j] = -1;
        printf("a[%d][%d] = %d \n", i, j, a[i][j]);

    }
}
return 0;
}

My seed looks like this:

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


// random seed
int GetRand(int min, int max);

int main(void)
{
  int i, r;
for (i = 0; i < 21; i++)
 {
r = GetRand(0, 100);
    printf("Your number is %d \n", r);
 }
 return(0);
 }

int GetRand(int min, int max)
{
static int Init = 0;
int rc;

if (Init == 0)
{
    srand(time(NULL));
    Init = 1;
}

rc = (rand() % (max - min +1) +min);

return (rc);
}

I know they're two different files, that's why there are to main functions. I'm just trying to figure out how a random seed can "override" the values of the 2D array.

I've been searching tutorials but all of them seem to be for C++ so that's why i;m asking here.

Any good advice?