why does the program exit without taking any input?

Question

I am trying to write a code to find the lowest grade among 10 quizzes and calculate the final grade of quiz, midterm and final exam.

This is the code. When i run it, it just says program finished with exit code 0.


#include <stdio.h>
#include <math.h>
int main(void)
{
    int i, quiz[i], min, QUIZ, final_grade;
    double MID, FINAL;
    
    
    /*loop store quiz grades*/
    for (i=1; i<=10; ++i)
    {   
        printf ("Enter quiz%d grade:", i);
        scanf ("%d", &quiz[i]);
    }
    
    /*store midterm and final value*/
    printf ("Enter midterm grade:");
    scanf ("%lf", &MID);
    printf ("Enter final exam grade:");
    scanf ("%lf", &FINAL);
    
    /*find sum of quiz score*/
    QUIZ=0;
    
    for (i=1; i<=10; ++i)
    {
        QUIZ += quiz[i];
    }
    printf ("%d",QUIZ);
    
    /*find min quiz score*/
    for (i=1; i<=10; ++i)
    {
        min=quiz[1];
        if (quiz[i]<min);
            min=quiz[i];
    }
    printf ("\n%d",min);
    
    /*calculate quiz pecent score*/
    QUIZ = 2.5*(QUIZ-min)/9;
    printf ("\n%d",QUIZ);
    
    /*calculate final grade*/
    if (MID>=FINAL)
    {
        final_grade=MID*.35+FINAL*.4+QUIZ;
    }
    else
    {
        final_grade=MID*.25+FINAL*.5+QUIZ;
    }
    printf ("\nThe final grade is:%d", final_grade);

    return 0;
}

It works fine in this part

{
    int i, quiz[i];
    /*loop store quiz grades*/
    for (i=1; i<=10; ++i)
    {    
        printf ("Enter quiz%d grade:", i);
        scanf ("%d", &quiz[i]);
    }
    int min;
    min=1;
    /*find min quiz grade*/
    if (quiz[i]<quiz[min])
        {
            min=i;
        }
    quiz[min]=0;
    printf ("%d", quiz[min]);
    
    
    return (0);
}

But when I add more work to the program it doesnt take input anymore.

Welcome to the world of *Undefined Behavior*. See: [Undefined, unspecified and implementation-defined behavior](https://stackoverflow.com/q/2397984/3422102) and [What is indeterminate behavior in C++ ? How is it different from undefined behavior?](https://stackoverflow.com/q/11240484/3422102) and [Undefined behavior](https://en.cppreference.com/w/c/language/behavior) — David C. Rankin, Feb 14 '22 at 06:11

score 2 · Answer 1 · answered Feb 14 '22 at 05:27

well stright off this is wrong

int i, quiz[i]

since you havent given i a value how big do you expect quiz to be

I changed to

int i, quiz[10]

after that it runs and gives me output, not sure if its the correct ouput though.

Enter quiz1 grade:3
Enter quiz2 grade:4
Enter quiz3 grade:5
Enter quiz4 grade:
5
Enter quiz5 grade:5
Enter quiz6 grade:5
Enter quiz7 grade:5
Enter quiz8 grade:5
Enter quiz9 grade:5
Enter quiz10 grade:5
Enter midterm grade:5
Enter final exam grade:6
47
5
11
The final grade is:15

score 1 · Answer 2 · answered Feb 14 '22 at 05:26

In your code

 int i, quiz[i], min, QUIZ, final_grade;

you are using i uninitialized. The value of i at that point is indeterminate. Your program behaviour is undefined, therefore.

You need to ensure to populate i with a valid value, before you can use that to define the VLA size.

score 1 · Answer 3 · edited Feb 14 '22 at 06:07

1

int i, quiz[i];

This is wrong. You have not given how big i, and therefore quiz, is supposed to be.

This is correct way:-

int i, quiz[5]; //you can change the size.

edited Feb 14 '22 at 06:07

David C. Rankin

81,885
6
58
85

answered Feb 14 '22 at 06:01

Samarth Matam

11
2

You can also do `i = 5, quiz[i];` and make `quiz` a VLA (*Variable Length Array*). Though note, after C11, the standard does not require VLAs be supported (but I don't know of any compiler that has chosen not to continue support - at least by extension) – David C. Rankin Feb 14 '22 at 06:09

score 0 · Answer 4 · answered Feb 14 '22 at 06:22

0

use the intialization with 0

int i = 0

then start the loop with i = 0 as well

for(i = 0 ; i <= 10 ; ++i)

And everything should be good to go

answered Feb 14 '22 at 06:22

Saumya Gautam

65
5

why does the program exit without taking any input?

4 Answers4