for loop will perform only one loop

Question

I need to make a C program to read the number of students(1<=students<=25) in a class and for every student to read his exam score ex 10/20 15/20 etc(1<=score<=20) and print the max and the max score of students and the average score of class.

I made the program but it performs the for loop only once for some reason.

Can you please help me understand why?

here is the code :

#include <stdio.h>

int main(void) {
    int m,i,b,sum,min,max,mo;
    sum=0;
    while (m<1 || m>25) {
            printf("give number of students ");
            scanf("%d",&m);
    }
    for (i=1; i<(m+1); i++) {
            while (b<1 || b>20) {
            printf("give score of  %d student",i);
            scanf("%d",&b);
            }

            if(i==1) {
                    min=b;
                    max=b;
            }
            else {
                    if(b<min) min=b;
                    if(b>max) max=b;
            }
            sum=sum+b;
    }
    mo=sum/m;
    printf("max is  %d and min is  %d and avg is  %d",max,min,mo);
}

Do you get any warnings when you compile this program? Have you tried to fix them? — Mark Byers, Nov 09 '12 at 18:36
You don't initialize `m`, so its value is *indeterminate*, i.e., it could be anything. You then proceed to check if it is less than 1 or greater than 25. Of course, at that point, it may or may not be. — Ed S., Nov 09 '12 at 18:36

score 1 · Answer 1 · answered Nov 09 '12 at 18:37

1

Not initialized the m and using in while condition

It is undefined behaviour using uninitialized local variable in conditon

Want to implement the same

use

do
{
  printf("give number of students ");
            scanf("%d",&m);
}
while(m<1 || m>25);

for (i=1; i<(m+1); i++) change the condition as i<=m It's the good technique rather < and then adding 1 Inside this loop use the same do while loop

answered Nov 09 '12 at 18:37

Omkant

9,018
8
39
59

but the problem is not there ... is in for loop which loops one time instead of m – user1809300 Nov 09 '12 at 18:41
same problem in for loop also ... now I edited see my answer now – Omkant Nov 09 '12 at 18:42
I think, You are doing same mistake at two places so I described one.. since the concept is same , so I think you got it didn't you ? – Omkant Nov 09 '12 at 18:43
I made this clear .. in this kind of situation always better to use do-while loop – Omkant Nov 09 '12 at 18:45

score 1 · Accepted Answer · answered Nov 09 '12 at 18:40

First - initialize your variables:

int m,i,b,sum,min,max,mo; // these are declared and uninitialized

m = 0;  // now it's initialized to 0
i = 0;
...

If you don't initialize them to something, you don't know what they are to start with.

Second - You need to change the value of b:

for (i=1; i<(m+1); i++) {
        while (b<1 || b>20) {  <-- here you're checking for b being valid
        printf("give score of %d student",i);
        scanf("%d",&b);
        }

So the first time in b will be between 1 and 20, if you don't reset it to something invalid you'll never get here again. After you record the value of b:

    sum=sum+b;
    b = 0;   // we're done with b for now, set it to something invalid for the while()
}

score 1 · Answer 3 · answered Nov 09 '12 at 18:42

1

You forgot to initialize the B variabkle, so it loops m times, never asking you to insert a score!

answered Nov 09 '12 at 18:42

alinsoar

15,386
4
57
74

score 1 · Answer 4 · edited May 23 '17 at 11:43

1. You initialize 'm' here, without any prior value

    int m,i,b,sum,min,max,mo;

2. Without a value, you check for this condition. Which means, a garbage value would be used. (May/May not fulfill your condition)

    while (m<1 || m>25) {

3. The crucial scanf for m is inside the previous while. Without which your FOR would run for a basic i=1 and stop.

    for (i=1; i<(m+1); i++) {

You need to understand about Garbage Values in C and vital step of initializing a variable to an initial value before using it.

You may read more on this link: What is a garbage value/How does it occur in C

for loop will perform only one loop

4 Answers4