折半查找
程序如下：
1 #include <stdio.h> 2 #include <stdlib.h> 3 #define N 5 4 int main() 5 { 6 int i,number,sign,top,bott,mid,loca,flag=1,a[N]; 7 char c; 8 printf("enter data:\n"); 9 scanf("%d",&a[0]); 10 i=1; 11 while(i<N){//输入已排好序的数 12 scanf("%d",&a[i]); 13 if(a[i] >= a[i-1]) 14 i++; 15 else 16 printf("enter this data again:\n"); 17 } 18 printf("\n"); 19 for(i=0;i<N;i++) 20 printf("%5d",a[i]); 21 printf("\n"); 22 while(flag){ 23 printf("input number to look for:"); 24 scanf("%d",&number); 25 sign=0;//sign为0表示还未找到 26 top=0; 27 bott=N-1; 28 if((number < a[0]) || (number > a[N-1])) 29 loca=-1;//表示找不到 30 while((!sign) && (top<=bott)){ 31 mid=(bott+top)/2; 32 if(number==a[mid]){ 33 loca=mid; 34 printf("has found %d,its position is %d\n",number,loca+1);//loca加一是为了符合阅读习惯 35 sign=1;//表示已找到 36 } 37 else if(number < a[mid]) 38 bott=mid-1; 39 else 40 top=mid +1; 41 } 42 if(!sign || loca==-1)//循环结束后，判断 43 printf("cannot find %d\n",number); 44 printf("contine or not(Y/N)?"); 45 scanf(" %c",&c); 46 if(c=='N'||c=='n') 47 flag=0; 48 } 49 system("pause"); 50 return 0; 51 }
