#include unsigned int round_up(unsigned int size) { return ( (size & 0x1) ? ((size >> 1) + 1) : (size >> 1) ); } unsigned int round_down(unsigned int size) { return ( size >> 1 ); } int binary_search(unsigned int key, unsigned int* array ,unsigned int size) { if (!array || size < 1) return -1; if (size == 1) return (*array == key); return ( binary_search(key, array, round_down(size)) || binary_search(key, array+round_down(size), round_up(size)) ); } int main(int argc,char* argv[]) { unsigned int array[] = {1,3,9,10,17,21}; if (binary_search(atoi(argv[1]),array, sizeof(array)/sizeof(*array) )) printf("Find it!\n"); else printf("Didn't find it!\n"); return 0; }