C language structure array pointer and function

Structure array pointer
Pointer variables can point to an array of structures , At this time, the value of the pointer variable is the first address of the entire array .
set up ps Is a pointer variable to the structure array , be ps It also points to the second row of the structure array 0 Elements ,ps+1
Point to first element ,ps+i Then point to the second i Elements , This is the same as the case of ordinary arrays .
【 Example 】 Output structure array with pointer variable .

 #include <stdio.h>

struct stu{
         int num;
         char *name;
         char sex;
         float score;
         } *ps, boy[5]={
                    {101, "Zhou ping", 'M', 45},
                    {102, "Zhang ping", 'M', 62.5},
                    {103, "Liou fang", 'F', 92.5},
                    {104, "Cheng ling", 'F', 87},
                    {105, "Wang ming", 'M', 58}
        };

int main(){
             printf("No\tName\t\tSex\tScore\t\n");
             for(ps=boy; ps<boy+5; ps++)
             printf("%d\t%s\t%c\t%f\t\n", ps->num, ps->name, ps->sex,
             ps->score);

            return 0;
}
Running results ：
No     Name    Sex Score
101 Zhou ping   M 45.000000
102 Zhang ping  M 62.500000
103 Liou fang   F 92.500000
104 Cheng ling  F 87.000000
105 Wang ming   M 58.000000
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It should be noted that , Although a structure pointer variable can be used to access structure variables or structure array elements
member , however , You can't make it point to a member . In other words, it is not allowed to take a member's address to give it . therefore ,
The following assignment is wrong ：
ps=&boy[1].sex;
And can only be ：
ps=boy; // Give the first address of the array
Or is it ：
ps=&boy[0]; // give 0 First address of element No
Structure pointer variables as function parameters
The structure variable represents the whole structure itself , Not the first address , The entire... Passed as a function parameter
Structure , That is, all the members . If the structure has more members , Especially when the members are arrays , Time and space of transmission
It's going to cost a lot , Seriously reduce the efficiency of the program . So the best way is to use pointers , That is, use pointer variables as
Function parameter . At this time, only the address is passed from the argument to the formal parameter , Very fast .

【 Example 】 Calculate the average score of a group of students and the number of failed students .

 #include <stdio.h>

#define STU struct stu
 STU{
     int num;
     char *name;
     char sex;
     float score;
     }boy[5]={
     {101,"Li ping",'M',45},
     {102,"Zhang ping",'M',62.5},
     {103,"He fang",'F',92.5},
     {104,"Cheng ling",'F',87},
     {105,"Wang ming",'M',58}
};

void average(STU *ps);

     int main(){
     STU *ps = boy;
     average(ps);
     return 0;
}

void average(struct stu *ps){
     int flunk=0, i;
     float sum=0;
         for(i=0; i<5; i++,ps++){
                 sum += ps->score;
                 if(ps->score < 60) flunk += 1;
         }
     printf("sum=%.2f, average=%.2f, flunk=%d\n", sum, sum/5, flunk);
}
Running results ：
sum=345.00, average=69.00, flunk=2

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