//二分查詢:

#include <stdio.h> int binsearch(int x, int v[], int n); main() {   int i, result, n;  int wait;    int x = 17; // 需要查詢的數值  int v[19]; // 定義一個數組  // 給陣列賦值  for(i = 0; i < 20; ++i)    v[i] = i;  /**  for(i = 0; i < 20; ++i)  printf("%d \n", v[i]);  */  n = 20;  result = binsearch(x, v, n);  printf("%d", result);  scanf("%d", &wait); } int binsearch(int x, int v[], int n) {  int low, high, mid;  low = 0;  high = n - 1;  while (low <= high)  {  mid = (low + high) / 2;  if(x < v[mid])   high = mid - 1;  else if (x > v[mid])   low = mid + 1;  else   return mid;  // 看看迴圈執行了多少次  printf("mid = %d, low = %d, high = %d \n", mid, low, high);  }  return -1; }  

// 二分查詢的變形：

#include<stdio.h> int main(){ int bs(int a[],int size,int p);  int i,n,result; int p=11; int size=20; int a[19]; for(i=1;i<=20;i++) a[i]=i; result=bs (a,size,p);     printf("%d",result);     return 0;         } int bs(int a[],int size,int p) {int l=0;int r=size-1; while(l<=r){ int mid=l+(r-l)/2; if(p==a[mid]) return mid; else if(p>a[mid]) l=mid+1; else r=mid-1;     printf("mid = %d,l= %d,r = %d\n",mid,l,r); }

return -1;         }