program not storing/returning array properly

Question

I am trying to write a simple program that stores an array and then returns it. However, it is not returning all of the numbers correctly, specifically toward the end of the array. Here is an example of the output:

Please enter number of numbers
5
Please enter number 1
2
Please enter number 2
3
Please enter number 3
5
Please enter number 4
6
Please enter number 5
7
Number 1 is 2
Number 2 is 3
Number 3 is 5
Number 4 is 14
Number 5 is 1
logout

[Process completed]

and here is my code:

#include <stdio.h>

int main (void) {
    int i, num;
    int x[num];

    printf("Please enter number of numbers\n");
    scanf("%d",&num);

    for (i = 0; i < num; i++) {
        printf("Please enter number %d\n", i + 1);
        scanf("%d",&x[i]);
    }
    for (i = 0; i < num; i++) {
        printf("Number %d is %d\n", i + 1, x[i]);
    }

    return 0;
}

regarding the calls to the scanf() function: the returned value (not the converted parameter value) needs to be checked to assure the input/conversion operation was successful — user3629249
– user3629249, Commented Apr 6, 2015 at 20:29

Srinath Mandava · Accepted Answer · 2015-04-06 19:22:12Z

2

Before scanning num you are doing int x[num] and as num stores garbage value you aren't getting the correct output.

int main (void) {
    int i, num;
   // int x[num]; // num is not defined here

    printf("Please enter number of numbers\n");
    scanf("%d",&num);
     int x[num];

    for (i = 0; i < num; i++) {
        printf("Please enter number %d\n", i + 1);
        scanf("%d",&x[i]);
    }
    for (i = 0; i < num; i++) {
        printf("Number %d is %d\n", i + 1, x[i]);
    }

    return 0;
}

answered Apr 6, 2015 at 19:22

Srinath Mandava

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3 Comments

Brian McFarland Over a year ago

Note: This is only valid C99 and later. Using malloc to allocate the array is far more portable. Which of the two is the "best practice" depends on industry / application.

Srinath Mandava Over a year ago

@BrianMcFarland Yeah... How is this implemented in C99..? Is the malloc indirectly called when we declare x[num] ?

Brian McFarland Over a year ago

In theory it could just be a stack pointer manipulation just like a fixed-size array. Hidden calls to malloc and free would also probably work. But most of my low level debugging experience is w/ C89 (or close to it), so I couldn't really tell you.

Pankaj Andhale · Accepted Answer · 2015-04-06 19:24:07Z

2

I think You should initialise the num variable so that it will not be having the garbage values initially..

answered Apr 6, 2015 at 19:24

Pankaj Andhale

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