6-10.c

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

#define MAXSIZE 10
#define NotFound 0
typedef int ElementType;

typedef int Position;
typedef struct LNode *List;
struct LNode {
    ElementType Data[MAXSIZE];
    Position Last; /* 保存线性表中最后一个元素的位置 */
};

List ReadInput(); /* 裁判实现，细节不表。元素从下标1开始存储 */
Position BinarySearch(List L, ElementType X);

int main() {
    List L;
    ElementType X;
    Position P;

    L = ReadInput();
    scanf("%d", &X);
    P = BinarySearch(L, X);
    printf("%d\n", P);

    return 0;
}

Position BinarySearch(List L, ElementType X) {
    int l = 0, r = L->Last;
    while (l <= r) {
        int m = l + (r - l) / 2;
        if (L->Data[m] == X)
            return m;
        else if (L->Data[m] < X)
            l = m + 1;
        else
            r = m - 1;
    }
    return NotFound;
}