array of struct C scanf with float - c

Question

hello im trying to work with a struct of students but everytime i ask the input of grade the program stop running and i dont know why. im using Turbo C++ 4.0. if i use grades as int the program doesnt stop but when i use them as float the program stop running. please any help heres the code:
#include<conio.h>
#include<stdio.h>
#define num 2
struct student {
char name[50];
float cal1;
float cal2;
float prom;
} est[num];
int main () {
int i=0;
clrscr();
for(i=0;i<=num;i++) {
printf("\nName of student[%d]:",i);
scanf("%s",&est[i].name);
printf("\nGrade #1 [%d]:",i);
scanf("%f",&est[i].cal1);
printf("\nGrade #2 [%d]:",i);
scanf("%f",&est[i].cal2);
}
for(i=0;i<=num;i++) {
printf("\nStudent [%d]:",i);
printf("\nName: ");
printf("%s",est[i].name);
printf("\nGrade #1: ");
printf("%f",est[i].cal1);
printf("\nGrade #2: ");
printf("%f",est[i].cal2);
}
getch();
return 0;
}

Answer 1

You define:
#define num 2
struct student { … } est[num];
and you loop on:
for (i = 0; i <= num; i++)
{
…scanning code…
}
This is a buffer overflow. It attempts to read 3 students worth of data, with the third student's data going into the space after the space allocated for est. This is a buffer overflow and leads to undefined behaviour; anything can happen and it is OK.
In C, get used to using the idiomatic for loop:
for (i = 0; i < limit; i++)
In the code that reads data, you need to check that the scanf() calls succeed:
printf("\nName of student[%d]:",i);
if (scanf("%s", est[i].name) != 1) // Note no & for strings
…handle error…
printf("\nGrade #1 [%d]:",i);
if (scanf("%f", &est[i].cal1) != 1)
…handle error…
printf("\nGrade #2 [%d]:",i);
if (scanf("%f", &est[i].cal2) != 1)
…handle error…
The printing loop should not attempt to print more entries than were actually read, which might be less than num if there was an error. Obviously, it needs to be in the idiomatic form too, but you should really be using:
int j;
for (j = 0; j < i; j++)
or something similar so if only 1 entry was read, you only print that one entry.

Answer 2

here is an example of the code that
cleanly compiles, links, runs
I did not use conio.h as it is non-standard
(and not available on my machine)
this code still needs the error checking for returned value from scanf added
#include <stdio.h>
//#include <conio.h>
#include <stdlib.h> // system()
#define num (2)
struct student
{
char name[50];
float cal1;
float cal2;
float prom; // only one ';'
};
// separated definition, above, from declaration, below
struct student est[num];
int main ()
{
int i=0;
system( "cls" );
//clrscr();
for(i=0;i<num;i++) // note correction to for statement
{
printf("\nName of student[%d]:",i);
scanf(" %49s", est[i].name); // note correction to format string
// and using array
// as degraded into pointer
// otherwise
// unknown where trying to place data
// added vertical spacing for readability
printf("\nGrade #1 [%d]:",i);
scanf("%f", &est[i].cal1);
// added vertical spacing for readability
printf("\nGrade #2 [%d]:",i);
scanf("%f", &est[i].cal2);
}
for(i=0;i<num;i++) // note correction to 'for' statement
{
printf("\nStudent [%d]:",i);
printf("\nName: ");
printf("%s",est[i].name);
printf("\nGrade #1: ");
printf("%f",est[i].cal1);
printf("\nGrade #2: ");
printf("%f",est[i].cal2);
}
getchar(); // this will input the final newline, so will exit immediately
//getch();
return 0;
} // end function: main