C语言控制流语句

---

title: 2017-10-18控制流

tags: binsearch else-if, shellsort, insertsort

grammar_cjkRuby: true

前段时间忙着别的事情，不得不说政府部门办事真的很mj，自己的博客计划也就搁浅了，继续加油，不要被自己一点点的努力感动

else-if 折半查找binsearch

将待查找数据先和中间进行比较，如果待查找数据等于中间数据则直接返回，如果小于中间数则继续在前一半数据中进行判断，如果大于中间数则继续在后一半数据中进行判断。重复进行循环，直至搜索完数据。

/***********************/
//章节：第三章else-if
//内容：binsearch
/***********************/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/stat.h>
#include<time.h>

#define MAX_ELEMENT 10000
#define LOOP 200000

int binsearch(int x,int v[],int n);//x is the element to search for ,n the length
int binsearch2(int x,int v[],int n);

int main(void){
	int testdate[MAX_ELEMENT];
	int index;		//index of element to search for
	int n = 200;    //element to search for
	int i;
	clock_t time_taken;//其实就是一个长整型，clock（）返回程序运行的滴答数，要得到秒数则除以CLOCKS_PER_SEC
	for(i = 0;i < MAX_ELEMENT; ++i){
		testdate[i]=i;
		//printf("%d\n", testdate[i]);
	}

	for(i = 0,time_taken = clock();i < LOOP;++i){
		index = binsearch(n,testdate,MAX_ELEMENT);
	}
	time_taken = clock() - time_taken;
	if(index < 0)
		printf("Element %d is not found in \n",n);
	else
		printf("Element %d is found at the index %d\n", n,index);
	printf("binsearch() took %lu clocks[%lu seconds]\n",time_taken,time_taken/CLOCKS_PER_SEC);

	for(i = 0,time_taken = clock();i < LOOP;++i){
		index = binsearch2(n,testdate,MAX_ELEMENT);
	}
	time_taken = clock() - time_taken;
	if(index < 0)
		printf("Element %d is not found in \n",n);
	else
		printf("Element %d is found at the index %d\n", n,index);
	printf("binsearch2() took %lu clocks[%lu seconds]\n",time_taken,time_taken/CLOCKS_PER_SEC);
}

int binsearch(int x,int v[],int n){
	int low,mid,high;
	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;
	}
	return -1;
}

int binsearch2(int x,int v[],int n){
	int low,mid,high;
	low = 0;
	high = n-1;
	mid = (low+high)/2;

	while(low <= high && x != v[mid]){
		if(x < v[mid])
			high = mid -1;
		else
			low = mid + 1;
		mid = (low+high)/2;
	}
	if (x == v[mid])
		return mid;
	else
		return -1;
}

插入排序

insertsort是最简单的排序方法，主要想法就是将一个新的数据插入已经排好顺序的序列中，从而获得一个长度加一的新序列。以下是一个简单的示意图。

希尔排序

希尔排序首先是将序列分为几组数据，然后依次对该组数据进行插入排序，然后不断组数不断减少，然后依次再对该组数据进行插入排序，我们把这个分组的个数叫增量，最后增量必须为1.

增量的取值规则为第一次取总长度的一半,第二次取一半的一半，直至增量为1

/***********************/
//章节：第三章控制流
//内容：shellsort，insertsort
/***********************/
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<sys/stat.h>

void insertsort(int a[],int n){
	int i,j,tmp;
	for(i = 1; i < n;i++){
		tmp = a[i];
		for(j = i-1;j >= 0&&a[j] > tmp;j--)
				a[j+1] = a[j];
		a[j+1] = tmp;
	}
}

void shellsort(int a[],int n){
	int i,j,gap,tmp;
	for(gap = n/2 ; gap > 0 ; gap /= 2){
		for(i = gap; i < n; i++){
			tmp = a[i];
			for(j = i - gap; j >= 0&&a[j] > tmp; j-=gap)
					a[j+gap] = a[j];
			a[j+gap] = tmp;
		}
	}
}

int main(void){
	int a[]={1,2,5,10,4,9,1,8},b[]={1,2,5,10,4,9,1,8};
	int n,i;
	n = 8;
	insertsort(a,n);
	for(i=0;i<n;i++){
		printf("%d\n",a[i]);
	}
	printf(">>>>>>>>>>>>\n");
	shellsort(b,n);
	for(i=0;i<n;i++){
		printf("%d\n",b[i]);
	}
}

各种控制流语句

if else / else if

while

for

do while

switch case

goto sw; sw:语句 //跳出多层循环语句