如何在c++链表中修改数据
How To Modify Data In a c++ Linked List
我在c++中使用链表的概念制作了一个学生记录系统。该程序将在三种不同的考试中获取学生证、姓名和分数。然后，它将根据这些考试成绩计算总百分比，并根据总百分比显示相关消息。程序正在运行，没有任何错误。
但是我希望student id是唯一的。例如，如果用户输入一个已经分配给前一个学生的学生id，那么它将显示一条消息，"请输入不同的id"。
我该怎么做呢?如有任何帮助，不胜感激。
struct student
{
int id;
char name[MAX];
string status;
double aggr;
int matric_marks, inter_marks, entryTest_marks;
};
struct node
{
struct student *data;
struct node *next;
node()
{
data = 0;
next = NULL;
}
};
struct student *readStudent()
{
clearWindow();
struct student *stdnt = new student;
gotoxy(33,8);cout<<"Student ID: ";
while(!(cin >> stdnt->id) || cin.peek() != 'n')
{
char ch;
cin.clear();
cout << "sorry";
while(cin.get(ch) && ch != 'n');
}
cin.ignore();
gotoxy(33,10);cout<<"Student Name: ";
cin.getline(stdnt->name, 50);
gotoxy(33,12);cout<<"Enter Matriculation Marks: ";
cin>>(stdnt->matric_marks);
gotoxy(33,14);cout<<"Enter Intermediate Marks: ";
cin>>(stdnt->inter_marks);
gotoxy(33,16);cout<<"Enter Entry Test Marks: ";
cin>>(stdnt->entryTest_marks);
stdnt->aggr = calculate_aggregiate(stdnt);
gotoxy(33,18);cout<<"Student Aggregate Marks: "<< stdnt->aggr;
if (stdnt->aggr >= 70)
{
gotoxy(33,20);cout<<"Student Registered In Electrical Engg";
}
else if (stdnt->aggr >= 60)
{
gotoxy(33,22);cout<<"Student Registered In Mechanical Engg";
}
else if (stdnt->aggr >=50)
{
gotoxy(33,24);cout<<"Student Registered In Computer Science";
}
else
{
gotoxy(33,20);cout<<"Sorry! The Student Doesnt Qualify";
}
return stdnt;
}
struct node *createDatabase(int size)
{
int i = 0;
struct node *head = NULL;
struct node *last = NULL;
for(i = 0; i < size; i++)
{
struct student *stdnt = readStudent();
struct node * current = new node;
current->data = stdnt;
current->next = NULL;
if(last)
last->next = current;
else
head = current;
last = current;
}
return head;
}
struct node *InsertRecord(struct node *head)
{
struct node *record = new node;
struct student *stdnt = readStudent();
record->data=stdnt;
record->next=head;
return record;
}
double calculate_aggregiate(struct student *stud)
{
student *stdnt = stud;
double aggr;
aggr = stdnt->matric_marks * 10/100 + stdnt->inter_marks * 50/100 +
stdnt->entryTest_marks * 40/100;
return aggr;
}
struct node *DeleteRecord(struct node *head)
{
clearWindow();
struct node *curr,*prev, *temp;
int tdata;
if(head==NULL)
{
gotoxy(33,10);cout<<"NO RECORDS TO DELETE......!";
}
else
{
gotoxy(33,10);cout<<"Enter Student ID To Be Deleted: ";
cin>>tdata;
prev=curr=head;
while((curr!=NULL)&&(curr->data->id!=tdata))
{
prev=curr;
curr=curr->next;
}
if(curr==NULL)
{
gotoxy(33,12);cout<<"The Requested ID Is Not Found...!";
}
else if(curr==head)
{
head=head->next;
gotoxy(33,12);cout<<"DATA DELETED....!";
}
else
{
prev->next=curr->next;
if(curr->next==NULL)
{
temp=prev;
}
gotoxy(33,12);cout<<"DATA DELETED....!"<<tdata;
}
delete(curr);
}
return head;
}
void ModifyRecord(struct node *head)
{
clearWindow();
int ch, sid;
struct node *current;
struct student *stdnt;
if (head==NULL)
{
gotoxy(33,8);cout<<"NO RECORD TO MODIFY..!";
}
else
{
gotoxy(33,8);cout<<"Enter Student ID To Modify: ";
cin>>sid;
current=head;
while((current!=NULL) && (current->data->id!=sid))
{
current=current->next;
}
if (current==NULL)
{
gotoxy(33,10);cout<<"The Requested ID is Not Found";
}
else if(current->data->id==sid)
{
gotoxy(33,10);cout<<"What Do You Want To Modify";
gotoxy(33,12);cout<<"1. Student's Name";
gotoxy(33,14);cout<<"2. Student's Matric Marks";
gotoxy(33,16);cout<<"3. Student's Intermediate Marks";
gotoxy(33,18);cout<<"4. Student's Entry Test Marks";
gotoxy(33,20);cout<<"Enter Your Choice: ";
cin>>ch;
switch(ch)
{
case 1 : gotoxy(33,22);cout<<"Enter New Name: ";
cin.getline(current->data->name, 50);break;
case 2 : gotoxy(33,22);cout<<"Enter New Matric Marks: ";
cin>>(current->data->matric_marks);break;
case 3 : gotoxy(33,22);cout<<"Enter New Intermediate Marks: ";
cin>>(current->data->inter_marks);break;
case 4 : gotoxy(33,22);cout<<"Enter New Entry Test Marks: ";
cin>>(current->data->entryTest_marks);break;
current->data->aggr = current->data->matric_marks * 10/100 + current->data- >inter_marks * 50/100 +
current->data->entryTest_marks * 40/100;
}
gotoxy(33,24);cout<<"RECORD MODIFIED....!";
}
}
}
void SearchRecord(struct node *head)
{
clearWindow();
int s_id;
struct node *current;
if (head==NULL)
{
gotoxy(33,8);cout<<"NO RECORD TO SEARCH..!";
}
else
{
gotoxy(33,8);cout<<"Enter Student ID To Be Searched: ";
cin>>s_id;
current=head;
while ((current!=NULL) && (current->data->id!=s_id))
{
current=current->next;
}
if (current==NULL)
{
gotoxy(33,10);cout<<"The Requested ID is Not Found";
}
else if (current->data->id==s_id)
{
gotoxy(33,10);cout<<"Student ID: "<<current->data->id;
gotoxy(33,12);cout<<"Student Name: "<<current->data->name;
gotoxy(33,14);cout<<"Student Matric Marks: "<<current->data->matric_marks;
gotoxy(33,16);cout<<"Student Intermediate Marks: "<<current->data - >inter_marks;
gotoxy(33,18);cout<<"Student Entry Test Marks: "<<current->data- >entryTest_marks;
gotoxy(33,20);cout<<"Student Aggregate Marks: "<<current->data->aggr;
if (current->data->aggr >= 70)
{
gotoxy(33,22);cout<<"Student Registered In Electrical Engg";
}
else if (current->data->aggr >= 60)
{
gotoxy(33,22);cout<<"Student Registered In Mechanical Engg";
}
else if (current->data->aggr >=50)
{
gotoxy(33,22);cout<<"Student Registered In Computer Science";
}
else
{
gotoxy(33,22);cout<<"Sorry! The Student Doesnt Qualify";
}
}
}
}
void print(struct node *head)
{
clearWindow_p();
struct node *current = head;
if (head == NULL)
{
gotoxy(33,8);cout<<"No Student Registered Yet......!";
}
else
{
cout<<"ntttttSTUDENTS STATISTICS";
while(current)
{
struct student *stdnt = current->data;
cout<<"nttttt-------------------------------- ";
cout<<"ntttttStudent ID :"<<stdnt->id;
cout<<"ntttttStudent Name :"<<stdnt->name;
cout<<"ntttttMatric Marks :"<<stdnt->matric_marks;
cout<<"ntttttIntermediate Marks :"<<stdnt->inter_marks;
cout<<"ntttttEntry Test Marks: "<<stdnt->entryTest_marks;
cout<<"ntttttAggregate: "<<stdnt->aggr;
if (stdnt->aggr >= 70)
{
cout<<"ntttttStudent Registered In Electrical Engg";
}
else if (stdnt->aggr >= 60)
{
cout<<"ntttttStudent Registered In Mechanical Engg";
}
else if (stdnt->aggr >=50)
{
cout<<"ntttttStudent Registered In Computer Science";
}
else
{
cout<<"ntttttSorry! The Student Doesnt Qualify";
}
current=current->next;
}
cout<<"nttttt--------------------------------";
}
}
int compareStudents(struct student *left, struct student *right)
{
return strcmp(left->name, right->name);
}
struct node *sort(struct node *head)
{
//using bubble sort
int swapped = 0;
do
{
swapped = 0;
struct node *current = head;
struct node *previous = NULL;
while(current && current->next)
{
if(compareStudents(current->data, current->next->data) > 0)
{
//swap here
struct node *next = current->next;
if(previous)
{
previous->next = next;
}
else
{
head = next;
}
current->next = next->next;
previous = next;
previous->next = current;
swapped = 1;
}
else
{
previous = current;
current = current->next;
}
}
} while(swapped);
return head;
}
int main()
{
system("color f0");
window();
SetColor(28);
int total,i,choice;
int x = 2;
struct node *head;
head=NULL;
do
{
menu:
gotoxy(x, 8);cout<<"1.Create a Record File";
gotoxy(x, 10);cout<<"2.Insert Student's Record";
gotoxy(x, 12);cout<<"3.Modify Student's Record";
gotoxy(x, 14);cout<<"4.Delete Student's Record";
gotoxy(x, 16);cout<<"5.Search Student's Record";
gotoxy(x, 18);cout<<"6.Print All Records";
gotoxy(x, 20);cout<<"7.Sort According To Names";
gotoxy(x, 22);cout<<"8.Clear The Screen";
gotoxy(x, 24);cout<<"9.Exit";
gotoxy(x, 26);cout<<"Enter your choice";
cout<<" [ ]bb";
cin>>choice;
switch(choice)
{
case 1:
clearWindow();
gotoxy(33, 8);cout<<"How Many Students Do You Want To Register: ";
cin>>total;
head=createDatabase(total);
break;
case 2:
head=InsertRecord(head);
break;
case 3:
ModifyRecord(head);
break;
case 4:
DeleteRecord(head);
break;
case 5:
SearchRecord(head);
break;
case 6:
print(head);
break;
case 7:
sort(head);
print(head);
break;
case 8:
main();
break;
default: gotoxy(33,8);cout<<"INVALID OPTION";
}
}while(choice!=9);
getch();
return 0;
}
既然使用的是c++，就应该充分利用内置类型。如果只有一个学生具有给定的ID，则使用std::map<>模板。例如:
struct student
{
char name[MAX];
string status;
double aggr;
int matric_marks, inter_marks, entryTest_marks;
};
map<int, student> students;
then，遍历学生:
for (auto i = students.begin(); i != students.end(); ++i) {
int studentId = i->first;
student& student = i->second;
student.aggr = ...
}
(auto是c++ 11，不是所有的编译器默认启用它。看到这里。)
如果你知道学生id的范围，并且它在一个可行的内存范围内，你可以使用UsedId[]数组
如果范围太大而无法保存，则使用Hashmap，(c++中的MAP)
我可能会实现一个叫做FindRecordByID的东西。
struct student *FindRecordByID(struct node *head, int id) {
for(; head != NULL; head = head->next)
if (head->data->id == id)
return head->data;
return NULL;
}
然后，当您执行create_new_student例程时，您可以使用它来验证给定的ID是否尚未使用。
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