Help with structures

[gordonfreeman]

Hi, I'm trying to understand how to use structures. I've written this code and it runs but when i try to modify the ID of a student in the structure the program crashes, up until that point it runs. Why ?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


struct student{
    int id;
    char name[100];
    int age;
};

void main(){
    struct student a;

    a.id=0;
    strcpy(a.name, "Andre");
    a.age=0;
    printf("%i\n%s\n%i\n", a.id, a.name, a.age);
    system("PAUSE");
    printf("enter a new id: ");
    scanf("%i\n", a.id);
    printf("ID: %i\n", a.id);
    system("PAUSE");
}

[Syscal]

You have to pass it as a pointer for scanf. Should be

scanf("%i", &a.id);

[gordonfreeman]

what a rookie mistake lol

[gordonfreeman]

OK so now that i have that I also need to be able to load an array of structures from a text file so I may need to spend some time understanding that one.... If anyone knows how i could go about doing this please don't hesitate to lend a helping hand :-D

[anduril462]

Start with a proper main function. Read this: FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com.

Then, to read a whole file, you'll need to know how to open and close it, and you'll need to know how to read out of it. Since it's a text-based data file, you should look into the scanf function. Also, since you're reading a whole file, presumably with more than one entry, you will need a loop.

I suggest you read some tutorials on file handling and loops in C (we have some on this site, and Google has plenty more). Post back your best effor we'll go from there.

[gordonfreeman]

OK i need to convert what i wrote so far into a system that simply takes input from a text file instead of from console input upon execution.


HERE's the code, it's very straightforward:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 4 //how many students u will enter


struct student{
    char last[100],first[100];
    int t1,t2,t3;
    float avg;
    char grade;
};

void load(struct student s[], int n){
    int i;
    for(i=0;i<n;i++){
        printf("Enter last name: ");
        gets(s[i].last);
        printf("enter first name: ");
        gets(s[i].first);
        printf("enter 3 scores");
        scanf("%d%d%d",&s[i].t1,&s[i].t2,&s[i].t3);
        //calc avg
s[i].avg=(s[i].t1+s[i].t2+s[i].t3)/(float)3;

if(s[i].avg>70)
    s[i].grade='p';
else
    s[i].grade='f';
fflush(stdin);
    }
}

void print(struct student s[], int n)
{
    for(int i=0;i<n;i++)
    {
        printf("first name is %s, last name is %s\n", s[i].first, s[i].last);
        printf("score 1 is %d, score 2 is %d, score 3 is %d\n", s[i].t1, s[i].t2, s[i].t3);
        printf("the average is %f\n", s[i].avg);
        printf("The grade is %c\n", s[i].grade);
    }
}

void sort(struct student s[], int n)
{
    int i, j;
    student t;
    for(i=0; i<n-1;i++)
        for(j=0;j<n-1;j++)
        {
            if (s[j].avg<s[j+1].avg)//decending order
            {
                t=s[j];
                s[j]=s[j+1];
                s[j+1]=t;
            }
        }
}

void passed(struct student s[], int n)
{
    int count=0;

    for(int i=0;i<n;i++)
    {
        if(s[i].grade=='p')
            count++;
        printf("passed count is %d\n", count);
    }
}

void main()
{
    student s[SIZE];
    load (s, SIZE);
    sort (s, SIZE);
    print (s, SIZE);
    passed (s, SIZE);
    system("PAUSE");
}

Any idea's on how i can take input from a text file instead of console?

[Syscal]

Start with this: C File I/O Tutorial - Cprogramming.com