Populate array unique

#include <stdio.h>
#include <string.h>
#include <math.h>
#define SIZE 20

//populate an array of given SIZE with unique numbers from 0 to SIZE-1.use rand()

void pop_arr(int *,int);
void pr_arr(int *, int);
void is_it_repeat(int *,int,int);

int main()
{
    int arr[SIZE];
    pop_arr(arr,SIZE);
    pr_arr(arr,SIZE);

    return 0;
}
void pr_arr(int *a,int s)
{
    int i;
    for(i=0;i<s;i++)
        printf("%d\t",a[i]);
    printf("\n");
}
void pop_arr(int *a,int s)
{
    int i,j,counter=0;
    for(i=0;i<s;i++)
    {
        printf("counter %d\n",counter);
        counter++;
        a[i] = rand()%SIZE;
        printf("\nvalue %d\t",a[i]);
        {
            for(j=0;j<=i-1;j++)//here suppose to start function
            {
                if(a[i]==a[j])
                    j = i,i--,printf("try once more!");
            }
        }

    }
}