while loop asks user input one time only

Question

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

struct the_struct
{
 char FirstName[20];
 char LastName[32];
 int  Score[20];
};
int main ()
{
int i,n;
struct the_struct *ptr[100];
printf("how many students?\n");
scanf("%d",&n);
while (i<=n);
   {
   i==0;
   ptr[i] = malloc(sizeof(struct the_struct));
   printf("Enter First Name \n");
   scanf("%s",ptr[i]->FirstName);
   printf("Enter Last Name \n");
   scanf("%s",ptr[i]->LastName);
   printf("Enter Score? \n");
   scanf("%s",ptr[i]->Score);
   printf("%s %s %s\n",ptr[i]->FirstName,ptr[i]->LastName,ptr[i]->Score);
   i++;
   }

}

hey guys, so when i enter the first input, it goes only once without going on for the number the user inputs, i tried the for loop but same result. still learning C so my apology if i misunderstood something.

Thanks in advance.

When i remove the ; when it asks for number of students it ends the program, but it allows me to enter a letter as a first name and ignoring the student number. — Ankosh
– Ankosh, Commented Apr 27, 2014 at 1:47

timrau · Accepted Answer · 2014-04-27 01:56:44Z

1

Your while loop is problematic. You could rewrite it as:

for (i = 0; i < n; ++i)
{
   ptr[i] = malloc(sizeof(struct the_struct));
   printf("Enter First Name \n");
   scanf("%s",ptr[i]->FirstName);
   printf("Enter Last Name \n");
   scanf("%s",ptr[i]->LastName);
   printf("Enter Score? \n");
   scanf("%s",ptr[i]->Score);
   printf("%s %s %s\n",ptr[i]->FirstName,ptr[i]->LastName,ptr[i]->Score);
}

And since you use %s to read and print Score, you should declare it as char Score[20]; instead of int.

edited Apr 27, 2014 at 1:56

answered Apr 27, 2014 at 1:46

timrau

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1 Comment

Ankosh Over a year ago

that worked!! i'm just printing to know the input is working or not. Thanks!!

Sergey Kalinichenko · Accepted Answer · 2014-04-27 01:45:07Z

0

The problem is that i is uninitialized. Therefore, the loop while (i <= n) has undefined behavior, and can end at any time.

Add int i = 0 initializer to fix this problem.

Notes:

i == 0 expression at the beginning of the loop has no effect
Since i starts at zero, your while loop should be while (i < n), not <=.
You should check the results of scanf to see if the user entered something meaningful
You should specify the size of the array into which you read a string, e.g. scanf("%31s",ptr[i]->LastName); This prevents buffer overruns.

answered Apr 27, 2014 at 1:45

Sergey Kalinichenko

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2 Comments

Ankosh Over a year ago

i changed the while loop like you said, same result. tried also the for loop same result.

Sergey Kalinichenko Over a year ago

@Ankosh You need to remove the semicolon after your loop, too. Here is a demo

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