Reverse a 2D array in C

Question

I'm trying to reverse my 2D array, I have this code with two functions, first one creates a random matrix of a rows and a columns, the second one must reverse it, but I don't quite understand what I did wrong there, because in the end it prints me just a row of numbers. Example: last number in the matrix is, let's say, 12, so it prints me: " 0 12 0 "

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

int ar[100][100];

void create_mat(int a)
{
    srand(time(NULL));
    for (int i=0; i<a; i++)
    {
        printf("\n");
        for (int j=0; j<a; j++)
        {
            ar[a][a]=rand()%15+1;
            printf("%d\t", ar[a][a]);
        }
    }
}
void reverse_mat(int a)
{
    printf("\nReversed: ");
    for (int i=0; i<a/2; i++)
    {
        printf("\n");
        for (int j=0; j<a; j++)
        {
            int temp = ar[a][a];
            ar[a][a]=ar[a-i-1][a];
            ar[a-i-1][a]=temp;
            printf("%d\t", ar[a][a]);
        }
    }
}

int main()
{
    int (*funcptr)(int);
    int (*rev)(int);
    funcptr = &create_mat;
    rev = &reverse_mat;
    int a;
    printf("Introduce the number of rows and columns: ");
    scanf("%d", &a);
    funcptr(a);
    rev(a);

    return 0;
}

Answer 1

Thank you to everyone for your help! Due to my pause in coding for a month, I've commited some errors that led to my problems, such as ar[a][a], rand()%15+1, etc. With your help and hints I fixed the program, and now it is doing what I was wanting it to do.

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

int ar[100][100];

void create_mat(int a)
{
    srand(time(NULL));
    for (int i=0; i<a; i++)
    {
        printf("\n");
        for (int j=0; j<a; j++)
        {
            ar[i][j]=rand()%16;
            printf("%d\t", ar[i][j]);
        }
    }
}
void reverse_mat(int a)
{
    for (int i=0; i<a/2; i++)
    {
        printf("\n");
        for (int j=0; j<a; j++)
        {
            int temp = ar[i][j];
            ar[i][j]=ar[a-i-1][j];
            ar[a-i-1][j]=temp;
        }
    }
}

void print_reversed(int a)
{
    printf("\nMatricea in forma inversa: ");
    for (int i=0; i<a; i++)
    {
        printf("\n");
        for (int j=0; j<a; j++)
        {

            printf("%d\t", ar[i][j]);
        }
    }
}

int main()
{
    int (*funcptr)(int);
    int (*rev)(int);
    int (*ptr_rev)(int);
    funcptr = &create_mat;
    rev = &reverse_mat;
    ptr_rev = &print_reversed;
    int a;
    printf("Introduceti nr de linii si coloane: ");
    scanf("%d", &a);
    funcptr(a);
    rev(a);
    ptr_rev(a);

    return 0;
}