In this article, I will show you, How to write a C program to print hollow rhombus star pattern.  Here, one thing is important to know that all sides of the square must be the same.

#include <stdio.h>

int main()
{
    int x = 0,y = 0;
    unsigned int rows = 0;

    printf("Enter the number of rows = ");
    scanf("%u",&rows);

    for(x=1; x<=rows; ++x)
    {
        // Print spaces
        for(y=1; y<= (rows - x); ++y)
        {
            printf(" ");
        }
        // Print stars
        for(y=1; y<=rows; ++y)
        {
            if((x==1) || (x==rows) || (y==1) || (y==rows))
            {
                //Print star
                printf("*");
            }
            else
            {
                //Print space
                printf(" ");
            }
        }
        // Print new line
        printf("\n");
    }
    return 0;
}

Output: