program returning garbage values even after declaring variables in c

Question

how do i correct this

i didn't use structure intentionally this is a program to input student's name, subject and marks. in the last block, the array (subject+f) 's 1st subscript is returning garbage values while the rest subscript are returning desired result. i have also posted the image of output as link.

#include<stdio.h>
#include<string.h>
int main()

{

int size,i,k,sub,a=0,reference;


    int temp,sorted;
    char temp_s[10];
    char temp_sb[10];

    printf("enter the size of class\n");
    scanf("%d",&size);
    printf("how many subjects are there?\n");
    scanf("%d",&sub);
    reference = sub;
    char name[size][20];
    char subject[size*sub][20];
    int marks[sub*size];
    int total,subtotal,retotal;
    for(k=0;k<sub;k++)
    {
    printf("so what's  the no. %d subject\n",k+1);
    scanf(" %s",(subject[k]));
    }

    for(i=0;i<size;i++)
        {

            int j,k=0;
            printf("Enter a name of student %d\n",i+1);
            scanf(" %s",(name+i));


                for(j=a;j<reference;j++)
                {
                    printf("enter marks of %s\n",(subject[k]));
                    scanf("%d",(marks+j));
                    k++;
                }

                a=j;
                reference=sub+j;


        }

    reference=sub;
    a=0;


    printf("\n list of students and marks:\n");
    for(i=0;i<size;i++)
        {
            int j,f=0;
            printf("%s\n",(name+i));
            for(j=a;j<reference;j++)
            {
                 printf("%s %d\n",(subject[f]),(marks[j]));
                 f++;
            }
            a=j;
            reference=sub+j;

        }
}

I suggest you take a debugger and step thru the program. There is definitely something wrong with your indexes. — Paul Ogilvie
– Paul Ogilvie, Commented Feb 21, 2018 at 9:10
Why don't you use subject[f]? I think subject is a char** and you want to have a char*... The two dimensional array is a Pointer to a Pointer. While you want to write in a char*. — NeverToLow
– NeverToLow, Commented Feb 21, 2018 at 9:18

Some programmer dude · Accepted Answer · 2018-02-21 09:28:54Z

2

Besides the problem with length of names and subjects, this here is a major problem:

(subject+k)

You are probably misunderstanding the subject[k] and *(subject + k) equivalent.

The variable subject is an array of arrays. That means subject[i] is an array (of char and can be used as a zero-terminated string).

The expression (subject + k) is a pointer to the array in subject[k]. It's equal to &subject[k] which have the type char (*)[10]. It's can not be used as a zero-terminated string without dereferencing. So either use *(subject + k) or the simple, less-to-write and easier-to-read subject[k].

edited Feb 21, 2018 at 9:28

answered Feb 21, 2018 at 9:21

Some programmer dude

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1 Comment

Aabshar Ahmed Over a year ago

i understand but it doesnt seem to have any difference to the result.. though i corrected it.

Stephen Docy · Accepted Answer · 2018-02-21 09:30:19Z

0

I think you also need to change

int marks[sub];

to

int marks[size * sub];

one mark for each subject for each student, correct?

answered Feb 21, 2018 at 9:30

Stephen Docy

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6 Comments

Aabshar Ahmed Over a year ago

it works now , but the code

for(j=a;j<reference;j++)                 {                     printf("enter marks of %s\n",(subject[k]));                     scanf("%d",(marks+j));                     k++;                 }

returns one extra loop when i take subject and size more than 2.

Stephen Docy Over a year ago

can you update the question with your current complete code?

Aabshar Ahmed Over a year ago

i updated it. it works fine as long as i not enter the size more than 2.

Stephen Docy Over a year ago

add this debug statement just before you prompt for the marks and I think you will see what is going on printf("%d..%d\n", j, reference);

Aabshar Ahmed Over a year ago

thankyou. the problem was with reference=reference + j; . so i changed it to reference=sub+j

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