什么时候需要用delete，已经没有使用产生什么后果，

#include<iostream>
#include"student.hpp"
using namespace std;
int main(){

student *head,*stu;
long del_num;
cout<<"input records:"<<endl;
head=creat();
print(head);
cout<<endl<<"input the deleted number:";
cin>>del_num;
head=del(head,del_num);
print(head);
cout<<endl<<"input the insert number:";
stu=new student;
cin>>stu->num>>stu->score;
while(stu->num!=0){
    head=insert(head,stu);
stu=new student;
cin>>stu->num>>stu->score;
}
    print(head);
return 0;   
}

#include<iostream>
using namespace std;
struct student{
long num;
float score;
student  *next;
   
};
int n;
student *creat(){
    student *head;
    student *p1,*p2;
    n=0;
    p1=p2=new student;
    cin>>p1->num>>p1->score;
    head=NULL;
    while(p1->num!=0){
        n=n+1;
        if(n==1)head=p1;
        else p2->next=p1;
        p2=p1;
        p1=new student;
        cin>>p1->num>>p1->score;
    }
    p2->next=NULL;
    return (head);
}
void print(student *head)
{
    student *p;
    cout<<endl<<"Now,These"<<n<<"records are:"<<endl;
    p=head;
    if(head!=NULL)
    do{
        cout<<p->num<<" "<<p->score<<endl;
        p=p->next;
    }while(p!=NULL);
}

 student * del(student *head,long num)

 {
     student *p1,*p2;
     if(head==NULL)
     {
         cout<<"list null"<<endl;return (head);
         
     }
     p1=head;
     while(num!=p1->num&&p1->num!=NULL)
     {
         p2=p1;
         p1=p1->next;
     }
     
     if(num==p1->num){
         if(p1==head)head=p1->next;
         else p2->next=p1->next;
         cout<<"delete:"<<num<<endl;
         n=n-1;
     }
     
     
     
     
     else
     cout<<"cannot find"<<num;
   
     return (head);
     

 }

 

 

 

 student *insert(student *head,student *stud)

 {
     student *p0,*p1,*p2;
     p1=head;
     p0=stud;
     if(head==NULL){
         head=p0;
         p0->next=NULL;
     }
     else{
     while((p0->num>p1->num)&&(p1->next!=NULL)){
         p2=p1;
         p1=p1->next;
     }   
     if(p0->num<=p1->num)
     {
         if(head==p1)head=p0;
         else p2->next=p0;
         p0->next=p1;
     }
     else{
         p1->next=p0;
         p0->next=NULL;
     }
         
         
         
         n=n+1;
         return (head);
         
         
         
         
         
     }

 }