课题名称：学生选修课程系统设计
说明：假定有n门课程，每门课程有课程编号，课程名称，课程性质，总学时，授课学时,实验或上机学时，学分，开课学期等信息，学生可按要求（如总学分不得少于60）自由选课。
要求：
1）系统以菜单方式工作
2）课程信息录入功能(课程信息用文 件保存)－－输入
3）课程信息浏览功能－－输出
4）查询功能：(至少一种查询方式)－－算法
5）按学分查询、按课程性质查询
6）学生选修课程统计信息
7）某门课程选修情况





#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct subjects
{
int num;
char name[20];
char kind[10];
int stime;
int ttime;
int etime;
int score;
int term;
struct subjects *next;
}SUB;

SUB *create_form()
{
SUB *head,*tail,*p;
int num,stime,ttime;
int etime,score,term;
char name[20],kind[10];
int size=sizeof(SUB);
head=tail=NULL;
printf("输入选修课程信息:\n");
scanf("%d %s %s %d %d %d %d %d",&num,&name,&kind,&stime,&ttime,&etime,&score,&term);
while(num!=0){
  p=(SUB *)malloc(size);
  p->num=num;
  strcpy(p->name,name);
  strcpy(p->kind,kind);
  p->stime=stime;
  p->ttime=ttime;
  p->etime=etime;
  p->score=score;
  p->term=term;
if(head==NULL)
  head=p;
else
  tail->next=p;
tail=p;
scanf("%d %s %s %d %d %d %d %d",&num,&name,&kind,&stime,&ttime,&etime,&score,&term);
}
tail->next=NULL;
return head;
}

void savefile(SUB *head)
{
SUB *p;
FILE *fp;
fp=fopen("subjects.txt","w");
fprintf(fp,"课程编号  课程名称  课程性质  总学时  授课学时  实验或上机学时  学分  开课学期\n");
for(p=head;p;p=p->next)
  fprintf(fp,"%5d%12s%9s%9d%9d%11d%11d%7d\n",p->num,p->name,p->kind,p->stime,p->ttime,p->etime,p->score,p->term);
fclose(fp);
}

void savefileadd(SUB *head)
{
SUB *p;
FILE *fp;
fp=fopen("subjectsadd.txt","w");
fprintf(fp,"课程编号  课程名称  课程性质  总学时  授课学时  实验或上机学时  学分  开课学期\n");
for(p=head;p;p=p->next)
  fprintf(fp,"%5d%12s%9s%9d%9d%11d%11d%7d\n",p->num,p->name,p->kind,p->stime,p->ttime,p->etime,p->score,p->term);
fclose(fp);
}

void savefiledel(SUB *head)
{
SUB *p;
FILE *fp;
fp=fopen("subjectsdel.txt","w");
fprintf(fp,"课程编号  课程名称  课程性质  总学时  授课学时  实验或上机学时  学分  开课学期\n");
for(p=head;p;p=p->next)
  fprintf(fp,"%5d%12s%9s%9d%9d%11d%11d%7d\n",p->num,p->name,p->kind,p->stime,p->ttime,p->etime,p->score,p->term);
fclose(fp);
}

void prin(SUB *head)
{
SUB *ptr;
if(head==NULL){
  printf("没有此门课程记录!\n");
  return;
}
printf("课程编号  课程名称  课程性质  总学时  授课学时  实践或上机学时  学分  开课学期\n");
for(ptr=head;ptr;ptr=ptr->next)
  printf("%5d%12s%9s%9d%9d%11d%11d%7d\n",ptr->num,ptr->name,ptr->kind,ptr->stime,ptr->ttime,ptr->etime,ptr->score,ptr->term);
}
void search(SUB *head)
{
int a,num;
int t=1;
char type[10];
char ch='a',ch1;
SUB *ptr;

while(ch!=' '){
  printf("若要按课程性质查找请输入1，若要按学分查找请输入2:\n");
  scanf("%d",&a);
  switch(a){
  case 1:printf("请输入要查找的课程的性质:\n");
   scanf("%s",type);
   printf("课程编号  课程名称  课程性质  总学时  授课学时  实践或上机学时  学分  开课学期\n");
   for(ptr=head;ptr;ptr=ptr->next)
    if(strcmp(type,ptr->kind)==0){
     printf("%5d%12s%9s%9d%9d%11d%11d%7d\n",ptr->num,ptr->name,ptr->kind,ptr->stime,ptr->ttime,ptr->etime,ptr->score,ptr->term);
           t=0;
    }
    if(t) printf("未找到!\n");
    t=1;
   break;
  case 2:printf("输入要查找的课程的学分\n");
   scanf("%d",&num);
   printf("课程编号  课程名称  课程性质  总学时  授课学时  实践或上机学时  学分  开课学期\n");
   for(ptr=head;ptr;ptr=ptr->next)
    if(ptr->score==num){
     printf("%5d%12s%9s%9d%9d%11d%11d%7d\n",ptr->num,ptr->name,ptr->kind,ptr->stime,ptr->ttime,ptr->etime,ptr->score,ptr->term);
                    t=0;
    }
    if(t) printf("未找到!\n");
    t=1;
  
}
printf("继续查找请按回车键，结束请按空格键:\n");
ch1=getchar();                           
ch=getchar();
}
}

SUB *insert(SUB *head)
{
SUB *ptr,*ptr2,*subj;
int size=sizeof(SUB);
char ch='a',ch1;
while(ch!=' '){
      subj=(SUB *)malloc(size);
      ptr=subj;
      printf("输入要插入的课程信息:\n");
      scanf("%d%s%s%d%d%d%d%d",&subj->num,subj->name,subj->kind,&subj->stime,&subj->ttime,&subj->etime,&subj->score,&subj->term);
       if(head==NULL){
         head=ptr;
         head->next=NULL;
    }
       else{
          for(ptr2=head;ptr2;ptr2=ptr2->next)
             if(ptr2->next==NULL){
             ptr2->next=subj;
             subj->next=NULL;
             break;
       }
    }
    printf("继续插入请按回车，结束请按空格:\n");
    ch1=getchar();                     
    ch=getchar();
    }
return head;
}
  



SUB *del(SUB *head)
{
SUB *p1,*p2;
char ch='a',ch1;
int num;
while(ch!=' '){
  printf("输入想要删除的课程编号:\n");
     scanf("%d",&num);
     if(head->num==num){
      p2=head;
      head=head->next;
      free(p2);
  }
     if(head==NULL)
      return NULL;
     p1=head;
     p2=head->next;
     while(p2){
    if(p2->num==num){
       p1->next=p2->next;
       free(p2);
    }
     else p1=p2;
     p2=p1->next;
  }
  printf("继续删除请按回车，结束请按空格:\n");
  ch1=getchar();                       //将回车键赋给CH1，否则num输完后再输入的回车键会赋给CH，因此用CH1填补。
  ch=getchar();
}
return head;
}

void choose(SUB *head)
{
SUB *p,*q;
int a[5];
int num,total=0,i=0,j;
printf("输入要选修的课程的编号，编号之间以空格分开，输完后以0结束\n");
scanf("%d",&num);
while(num!=0){
  for(p=head;p;p=p->next)
   if(p->num==num){
    total=total+p->score;
    a=num;
    i++;
   }
   scanf("%d",&num);
}
if(total<60) printf("选修总学分未达到60,选修失败!\n");
else {
  printf("选修成功!\n");
  printf("您选修的课程为:\n");
for(j=0;j<i;j++)  
    for(q=head;q;q=q->next)
    if(q->num==a[j])
     printf("%s  ",q->name);    }
}

void main()
{
SUB *head=create_form();
savefile(head);
prin(head);
search(head);
head=insert(head);                        //注意此处的必要性，函数insert的的返回值重新赋给head!
savefileadd(head);
printf("修改后的信息为:\n");
prin(head);
head=del(head);                           //注意此处的必要性，函数del的的返回值重新赋给head!
savefiledel(head);
printf("修改后的课程信息为:\n");
prin(head);
choose(head);
}