在C中输入的结构和值

Question

I have a program that does not work. The problem for example is:

You input 2 for students, then enter mark 5 for the first student and then 10 for second student.

The output sum in the fun() function should return 15 . But instead, it returns 20.

This is my code so far:

struct mark{
   int x;   
};

int main(){
    int n;
    printf("Enter the number of student: ");
    scanf("%d",&n);

    struct mark *marks= malloc(n * sizeof(struct mark)); ;

    for (int i = 0; i < n; i++ ){
        printf("Enter mark: ");
        scanf("%d",&(*marks).x);
    }

   fun(marks,n);

    free(marks);
    return 0;
}

void fun(struct mark *marks, int n){
    int sum =0,i;
    for (i = 0; i < n; i++ ){
        sum= sum+(*marks).x;

    }
    printf("Sum: %d \n",sum);

}

Answer 1

    scanf("%d",&(*marks).x);

Means you are reading into the first mark in marks .

You already have a for loop and a counter variable for reading into it, so use it. change

sum= sum+(*marks).x;

to

sum= sum+marks[i].x;

which is also equivalent to

sum = sum+(*marks+i).x;

Do the same for

scanf("%d",&(*marks).x);

change it to

scanf("%d",&marks[i].x);

again,

marks[i].x is equivalent to (*marks+i).x

The point is that you want to access the second mark in marks in your second iteration of your for loop. Also, don't forget to free() your marks when your program is done.

Answer 2

change :

scanf("%d",&marks[i].x);

and:

sum= sum+marks[i].x;

Answer 3

Inside main in this piece of code:

 for (int i = 0; i < n; i++ ){
        printf("Enter mark: ");
        scanf("%d",&(*marks).x);
    }

You are always assigning mark to 1st array element.

Inside fun in this piece of code:

for (i = 0; i < n; i++ ){
        sum= sum+(*marks).x;
    }

you are not iterating over the marks array, but instead always reading 1st array value.