1.输出S的值，精度1e-6

#include <stdio.h>

int main() {
	int i=1;
	double flag=1.0/(2*i-1)*2*i/(2*i-1);
	double sum=0;
	while(flag>1e-6) {
		sum+=flag;
		i++;
		flag=1.0/(2*i-1)*2*i/(2*i-1);
	}
	printf("%lf",sum);
}

2.编写函数，对n个字符串按字典顺序排序限定函数名void sort(char st[ ][10], int n)

#include <stdio.h>

void strcpy(char *str1,char *str2) {
	int i=0;
	while(str1[i]!='\0') {
		str2[i]=str1[i];
		i++;
	}
	str2[i]='\0';
}

int strcmp(char *str1,char *str2) {
	int i=0;
	while(str1[i]!='\0'&&str2[i]!='\0') {
		if(str1[i]>str2[i])
			return 1;
		else if(str1[i]<str2[i])
			return -1;
		else
			i++;
	}
	if(str1[i]=='\0'&&str2[i]=='\0')
		return 0;
	else if (str1[i]=='\0')
		return -1;
	else
		return 1;
}


void sort(char st[][10],int n) {
	char temp[10];
	for(int i=0; i<n-1; i++)
		for(int j=0; j<n-i-1; j++)
			if(strcmp(st[j],st[j+1])==1) {
				strcpy(st[j],temp);
				strcpy(st[j+1],st[j]);
				strcpy(temp,st[j+1]);
			}
}

int main() {
	char st[][10] = {"hello", "world", "python", "C", "java", "R"};
	int n = 6;
	sort(st, n);
	for (int i = 0; i < n; i++)
		printf("%s ", st[i]);
	printf("\n");
	return 0;
}

3.编写递归函数，实现对有序数组的二分查找

#include <stdio.h>

int search(int *a,int left,int right,int key) {
	while(left<=right) {
		int mid=(left+right)/2;
		if(a[mid]==key)
			return mid;
		else if(a[mid]<key)
			return (a,mid+1,right,key);
		return(a,left,mid-1,key);
	}
	return -1;
}

4.成绩信息包含：姓名，学号，讨论成绩，报告成绩，测试成绩五项信息，规定：
实验成绩 = 讨论成绩（20%）+报告成绩（20%）+测试成绩 （60%）
1）创建结点类型；
2）假如所有信息都存储在文件2018.txt中，创建链表；
3）对题中的里链表按实验成绩，从高到低排序

#include <stdio.h>
#include <stdlib.h>

typedef struct node {
	char name[20];
	int num;
	int repscore;
	int expscore;
	int testscore;
	struct node *next;
} node;

struct node *create() {
	FILE *file;
	if((file=fopen("2018.txt","r"))==NULL) {
		printf("open error");
		exit(0);
	}
	struct node *head=(struct node*)malloc(sizeof(struct node));
	head->next=NULL;
	struct node *p;
	while(!feof(file)) {
		p=(struct node *)malloc(sizeof(struct node));
		fscanf(file,"%s %d %d %d %d",&p->name,&p->num,&p->repscore,&p->expscore,&p->testscore);
		p->next=head->next;
		head->next=p;
	}
	fclose(file);
	return head->next;
}

struct node *sort(struct node *head) {
	if(head==NULL||head->next==NULL)
		return head;
	struct node *dummyhead=(struct node *)malloc(sizeof(struct node));
	dummyhead->next=head;
	struct node* p=head->next,*pre=dummyhead;
	while(p!=NULL) {
		struct node *temp=p->next;
		while(pre->next!=NULL&&pre->next->expscore>p->expscore)
			pre=pre->next;
		p->next=pre->next;
		pre->next=p;
		p=temp;
		pre=dummyhead;
	}
	return dummyhead->next;
}