c语言编程实现“折半查找”的过程。

//参考代码如下：

#include <stdio.h>

int main()

{

int i, j, n, k=0, isFound=0

int num[15] = {88,86,75,74,61,56,52,43,39,34,31,22,18,16,8} //测试数组

printf("请输出一个整数：\n")

scanf("%d", &n)

i = (int)15/2 //对折位移量

j = (int)15/2 //取数“指针”

while(k<2)

{

i = (int)i/2

if(i == 0) k++//i==0 即折半到无可再折时，仍有最后一次比较，故以k做计数

//若未相等，计算下一循环指针的位置

if(n<num[j])

j = j + (i + 1)

else if(n>num[j])

j = j - (i + 1)

else

{

isFound = 1

break //若找到相等数，标记已找到并退出循环

}

}

//输出结果

if(isFound)

printf("该数是数组中第%d个元素的值\n", j)

else

printf("查无此数！\n")

return 0

}

#include<stdio.h>

int find(int a[],int x,int n,int m)

{int i

if(n>m)return -1

i=(n+m)/2

if(a[i]==x)return i

if(a[i]>x)return find(a,x,n,i-1)

return find(a,x,i+1,m)

}

int main()

{

int a[20]={2,3,6,7,12,18,19,21,25,28,30,33,37,39,42,45,47,49,50,51}

int x,i

printf("已有的数是：\n")

for(i=0i<20i++)

printf("%d ",a[i])

printf("\n请输入要查找的数：")

scanf("%d",&x)

if((i=find(a,x,0,19))>=0)

printf("%d是第%d个数\n",x,i+1)

else printf("未找到%d\n",x)

return 0

}

#include<stdio.h>

int main()

{

char a[12]="abcdefklmnp",ch

int i,top,bot,mid

printf("Input a character\n")

scanf("%c",&ch)

printf("ch=%c\n",ch)

top=11

bot=0

mid=(top+bot)/2

while(bot<=top&&a[mid]!=ch)

{if(a[mid]>ch)top=mid-1

else if(a[mid]==ch)break

else bot=mid+1

mid=(top+bot)/2 

}

if(a[mid]==ch)printf("第%d个字符就是%c\n",mid+1,ch)

if(bot>top)printf("该字符不存在a中\n")

return 0

}

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