折半查找

程序如下：

#include <stdio.h>
#include <stdlib.h>
#define N 5
int main()
{
    int i,number,sign,top,bott,mid,loca,flag=1,a[N];
    char c;
    printf("enter data:
");
    scanf("%d",&a[0]);
    i=1;
    while(i<N){//输入已排好序的数
        scanf("%d",&a[i]);
        if(a[i] >= a[i-1])
            i++;
        else
            printf("enter this data again:
"); 
    }
    printf("
");
    for(i=0;i<N;i++)
        printf("%5d",a[i]);
    printf("
");
    while(flag){
        printf("input number to look for:");
        scanf("%d",&number);
        sign=0;//sign为0表示还未找到
        top=0;
        bott=N-1;
        if((number < a[0]) || (number > a[N-1]))
            loca=-1;//表示找不到
        while((!sign) && (top<=bott)){
            mid=(bott+top)/2;
            if(number==a[mid]){
                loca=mid;
                printf("has found %d,its position is %d
",number,loca+1);//loca加一是为了符合阅读习惯
                sign=1;//表示已找到
            }
            else if(number < a[mid])
                bott=mid-1;
            else
                top=mid +1;
        }
        if(!sign || loca==-1)//循环结束后，判断
            printf("cannot find %d
",number);
        printf("contine or not(Y/N)?");
        scanf(" %c",&c);
        if(c=='N'||c=='n')
            flag=0;
    }
    system("pause");
    return 0;
}