Hello there

I am stuck on how to use nest while!! This is the question:

Write a program that reads in two integers m and n, and prints out an m-by-n rectangle of
asterisks.
(a) Use two nested while loops.
(b) Use two nested for loops.

I did the for loops okay but cannot figure out how the while works.

Code:
#include <stdio.h>
int main()
{
    int m, n;
    int i=0;
    int j=0;


    printf("Input value for m and n: \n");  //prompts
    scanf("%d %d", &m, &n);                 //inputs


    while(i <= m)                           // Size of m
    {
        i++;
        printf("*");
    }


    while(j < n)
    {
       j++;
       printf("*");
    }


    return 0;
}

What am i doing wrong?