CareerCup

http://www.codeguru.com/forum/archive/index.php/t-341247.html

#include <stdio.h>

int main()
{
unsigned int n = 1;
char *p;

p = (char*)&n;
if (*p == 1)
printf("Little Endian\n");
else if (*(p + sizeof(int) - 1) == 1)
printf("Big Endian\n");
else
printf("What the crap?\n");

return 0;

int num=1;
if(*(char*)&num==1)
printf("Little Endian");
else
printf("Big Endian");

Nishant's answer can be found in C Programming FAQs. In addition to his answer, FAQ has the union version.

union {
int i;
char c[size(int)];
} x;

x.i = 1;
if (x.c[0] == 1)
printf("Little-endian\n");
else
printf("Big-endian\n");

unsigned int* x;
unsigned char *y;
*x = 0x00FF;
y=(char*)x;
if(*y == 0xFF)
//Little Endian
else
//Big Endian

int x = 0x1;
printf("\n\n%s\n\n", *((char*)&x) ? "Little Endian" : "BIG Endian");