Print the largest perfect square within given range

largest_perfect_square.c

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

int main(int argc, char** argv)
{
        if (argc < 2) {
                printf("usage: %s <limit>\n", argv[0]);
                return 1;
        }
        
        unsigned int i, n, limit = atoi(argv[1]);
        for (i = 1, n = i * i; n <= limit; i++)
                n += (2 * i) + 1;
        n -= (2 * --i) + 1;
        
        printf("%d: %d\n", i, n);
        
        return 0;
}