二分探索を実装してみましょうかという感じ。バグがありそうな気がしている。

gistfile1.c

#include <stdio.h>

void showList(char** list, size_t length)
{
	printf("%d: ", length);
	for(int i=0; i<length; i++)
		printf("%s, ", list[i]);
	printf("\npivot: %s\n\n", list[length/2]);
}

char* finder(char* target, char** list, size_t length)
{
	showList(list, length);

	if(length == 0)
		return NULL;

	int diff = strcmp(target, list[length/2]);

	if(diff == 0)
		return list[length/2];

	if(diff > 0)
		return finder(target, &list[length/2 + 1], length/2 - 1 + length%2);
	else
		return finder(target, list, length/2);
}

int main()
{
	char target[] = "dave";
	char* list[] = {"alice", "bob", "charlie", "dave", "ellen"};

	printf("result = %s\n", finder(target, list, sizeof(list)/sizeof(char*)));
	return 0;
}