C : program to calculate GPA for students - c

Question

Whenever I insert 2 or more students, the program gives the same gpa from the first student. I insert for both every time, and how can I display the max gpa and who got it?
#include <stdio.h>
FILE *f;
struct student
{
char name[20];
int id;
int n;
float sum;
float gpa;
} s[100];
float FUN_GPA(int n);
int main ()
{
int m,i,x,b;
float max=0;
s[i].sum=0;
printf("Please Enter Number Of Students : ");
scanf("%d",&m);
for(i=0;i<m;i++)
{
printf("\nStudent %d : \n",i+1);
printf("Name : ");
scanf("%s",&s[i].name);
printf("ID : ");
scanf("%d",&s[i].id);
printf("Number Of Courses : ");
scanf("%d",&s[i].n);
}
printf("\nEnter Student Marks");
for(i=0;i<m;i++)
{
printf("\n\n\t\t\t......[ Student %d ]......\n",i+1);
for(x=0;x<s[i].n;x++)
{
printf("Course %d Mark : ",x+1);
scanf("%d",&b);
s[i].sum+=b;
}
printf("\nSum Of The Courses Marks = %3.f",s[i].sum);
printf("\nGPA For Student %d = %f",i+1,FUN_GPA(s[i].gpa));
}
if (s[i].gpa>max)
max=s[i].gpa;
printf("\n\nHighest GPA is done by Student %d with GPA = %f",i,max);
{
if((f=fopen("d:\\STUDENTS.txt","w"))==NULL)
printf("\ncant open file ");
// if((f=fopen("d:\\STUDENTS.txt","r"))==NULL)
// printf("\ncant open file ");
fprintf(f,"Name : %s\t ID : %d\t GPA = %f \n",s[i].name,s[i].id,s[i].gpa);
fclose(f);
}
}
float FUN_GPA(int i)
{
s[i].gpa=0;
s[i].gpa=s[i].sum/s[i].n;
return s[i].gpa;
}

Answer 1

Replace FUN_GPA(s[i].gpa) by FUN_GPA(i).
Put this inside the loop; not much use having it outside:
if (s[i].gpa>max)
max=s[i].gpa;
The same applies to this initializer, by the way:
s[i].sum=0;
In general, do not use variable i outside the loop; this is bad practice and in your particular case, totally wrong!
i is not the index of the best performing student; it is not even a correct index once the loop ends, since it refers to the array element immediately following the last registered student. Please introduce a new variable to keep track of the index of the best performer so far. Instead of i, use this new variable in the lines to follow:
fprintf(f,"Name : %s\t ID : %d\t GPA = %f \n",s[i].name,s[i].id,s[i].gpa);
Same here; do not forget to add 1 like you did everywhere else already!
printf("\n\nHighest GPA is done by Student %d with GPA = %f",i,max);
General advice: use descriptive names. i is OK afaic; s and n are not so great, m, x and b would have been good for 50 lashes from my old teachers for sure!

Answer 2

This needs to be in a for loop (you're only checking one as it is currently written):
if (s[i].gpa>max)
max=s[i].gpa;
You'll probably also want to keep track of which i had the max.
So something like:
int iwithmax;
for ( i = 0 ; i < m ; i++) {
if (s[i].gpa > max) {
max = s[i].gpa;
iwithmax = i;
}
}
and change print statement accordingly:
printf("\n\nHighest GPA is done by Student %d with GPA = %f",iwithmax,max);