錯誤：使用struct type value（（*; ptr; ptr ++）需要標量）

Question

請您解釋此錯誤背後的原因。

錯誤代碼：

used struct type value where scalar is required for(;*ptr;ptr++) "for the below code?

是否有任何理由，我們是不允許結構變量在for循環？

#include<stdio.h> 
#include<stdlib.h> 
struct student 
{ 
     char name[20]; // Given 
     int math; // Marks in math (Given) 
     int phy; // Marks in Physics (Given) 
     int che; // Marks in Chemistry (Given) 
     int total; // Total marks (To be filled) 
     int rank; // Rank of student (To be filled) 
}; 

static int count=1; 
void enter_data(struct student* arr,int num); 
void print_data(struct student* arr,int num); 
int main() 
{ 
     int num=1; 
     char ch; 
     printf("Enter the number of student records you want to input?..\n"); 
     scanf("%d",&num); 

     struct student *arr=(struct student*)malloc(num*sizeof(struct student)); 



     printf("Do you want to enter the student record...(Y/N)\n"); 
     scanf(" %c",&ch); 
     if(ch=='y'||ch=='Y') 
     { 
       enter_data(arr,num); 
       printf("The created record is .....\n"); 
       print_data(arr,num); 

     } 
     else 
       return 0; 


} 

void enter_data(struct student* arr,int num) 
{ 
     int i; 
     struct student* ptr=arr; 
     for(;count<=num;ptr++,count++) 
     { 
       printf("Enter the name of the candidate...\n"); 
       scanf("%s",ptr->name); 
       printf("Enter the marks scored in maths,phy,che....\n"); 
       scanf("%d%d%d",&ptr->math,&ptr->phy,&ptr->che); 
       ((ptr->total)=(ptr->math)+(ptr->phy)+(ptr->che)); 

     } 
} 

void print_data(struct student* arr,int num) 
{ 
     int i; 
     struct student* ptr=arr; 
     for(;*ptr!=NULL;ptr++)//error here 
     { 
       printf("Name of the candidate...%s\n",ptr->name); 
       printf("Enter the marks scored in maths...%d\t physics... %d\tche... %d\n total=%d\n",ptr->math,ptr->phy,ptr->che,ptr->total); 

     } 
} 

Answer 1

遞增指針，即引用指向特定地址處的值而不是該指針地址處的值。 *ptr!=NULL意味着您在`* PTR！= NULL`結構的學生比較NULL

for(;ptr!=NULL;ptr++)//error fixed here 
      { 
        printf("Name of the candidate...%s\n",ptr->name); 
        printf("Enter the marks scored in maths...%d\t physics... %d\tche... %d\n total=%d\n",ptr->math,ptr->phy,ptr->che,ptr->total); 

      }