[Novice] error with output in C program

Question

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Program to read and write the array:

error with the output
No. of digits scanned != No. of digits printed

What I have tried:

#include <stdio.h>

int main()
{
    int x;
    int arr[x];
    int i;
    printf("Enter the value of 'x'\n");
    scanf(" %d", &x);
    printf("Enter %d elements\n",x+1);
    for(i=0;i<x;i++)
    {
        scanf(" %d\n", &arr[i]);
    }
    printf("the digits you entered are as follows: \n");
    for(i=0;i<x;i++)
    {
        printf("%d\t",arr[i]);
    }

    return 0;
}

Posted 10-Dec-17 0:27am

shreyas s

Updated 10-Dec-17 6:16am

v2

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3 solutions

Solution 1

You can't create an array with dynamic size before knowing that size.

C++

int x;
int arr[x]; // you create the array here
int i;
printf("Enter the value of 'x'\n");
scanf(" %d", &x); // you know the array size here

Advice: use the debugger to check that anything goes as expected.
There is a tool that allow you to see what your code is doing, its name is debugger. It is also a great learning tool because it show you reality and you can see which expectation match reality.
When you don't understand what your code is doing or why it does what it does, the answer is debugger.
Use the debugger to see what your code is doing. Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't find bugs, it just help you to. When the code don't do what is expected, you are close to a bug.

Posted 10-Dec-17 1:27am

Patrice T

Comments

shreyas s 11-Dec-17 1:22am

Thank you

Patrice T 11-Dec-17 1:28am

You welcome.

Solution 2

You really need to get hold of a good book on C programming, something like The C Programming Language, by Brian W. Kernighan & Dennis M. Ritchie[^]. You will learn much faster from a book or on-line tutorials. These forums are not designed to teach you programming.

Posted 10-Dec-17 1:31am

Richard MacCutchan

Comments

shreyas s 10-Dec-17 10:31am

Yeah, I tried reading that book but understanding the concepts wasn't easy for me:( So I opted to learn from online resources.
I apologize for bothering people here with my silly questions, and also do you know any place(website) on the internet where noobs like me can ask questions like these?

Richard MacCutchan 10-Dec-17 10:51am

You misunderstand the point I am trying to make. You will learn much better from a proper book or online tutorial. Once you have followed a formal tutorial then simple question like this will not give you trouble.

shreyas s 11-Dec-17 1:24am

Oh, I see what you mean.
Thanks for the advice:)

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CPallini · Accepted Answer · 2017-12-10T03:22:00

As others already noted, you need to create the array after you know its size. With a C99 compliant compiler (like GCC) you may write:
Please note: in order to simplify the code, I have omitted checking the scanf return value. You should always perform such a check in the actual code.

C

#include <stdio.h>

int main()
{
    int x;
    int i;

    printf("Enter the value of 'x'\n");
    scanf("%d", &x);

    int arr[x]; // here you know the array size.

    printf("Enter %d elements\n",x);
    for(i=0;i<x;i++)
    {
        scanf("%d", &arr[i]);
    }
    printf("the digits you entered are as follows: \n");
    for(i=0;i<x;i++)
    {
        printf("%d\t",arr[i]);
    }
    printf("\n");
    return 0;
}

On the other hand, with a not-C99-compliant compiler you have to write something like:

C

#include <stdio.h>
#include <stdlib.h>
int main()
{
    int x;
    int i;

    printf("Enter the value of 'x'\n");
    scanf("%d", &x);

    int * arr = (int *) malloc( sizeof(int) * x); // dynamically allocate memory on the heap
    if ( ! arr ) return -1;

    printf("Enter %d elements\n",x);
    for(i=0;i<x;i++)
    {
        scanf("%d", &arr[i]);
    }
    printf("the digits you entered are as follows: \n");
    for(i=0;i<x;i++)
    {
        printf("%d\t",arr[i]);
    }
    printf("\n");

    free (arr); // release the heap allocated memory

    return 0;
}