折半查找

bin_search(int A[],int n,int key){
int low,high,mid;
low = 0;
high = n-1;
while(low<=high)
{
mid = (low + high)/2;
if(A[mid]==key) return mid;
if(A[mid] low = mid +1;
   }
   if(A[mid]>key){
high = mid -1;
   }
}
return -1;
}

void zheban()
{
int A[10] = {2,3,5,7,8,10,12,15,19,21},i,n,addr;
printf("The contents of the Array A[10] are\n");
for(i=0;i<10;i++)
printf("%d ",A[i]);                           /*显示A内容*/
printf("\nPlease input a int for search\n");
scanf("%d",&n); 
addr =  bin_search(A,10,n);        /*返回下标*/
if(-1 != addr)                             /*查找成功*/
   printf("%d is the %dth unit \n",n,addr);
else  printf("There is no %d in array A\n",n);
}