Allocation of array size dynamically

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February 10th, 2013, 11:53 AM

Technovicez

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Allocation of array size dynamically

can't we allocate arraysize dynamically?
i have two compilers devc++ and ms visualstudio.when i compiled the below program in these two compilers ,dev c++ allowed dynamic allocation of array whereas ms visual studio raised an error
i.e unknown size of the array.
Why it raised this sort of error.
The program is

Code:

#include<stdio.h>
#include<conio.h>

    void change_it(int a)
    {
         a = 555;
}
/*bubble sort*/
void bubblesort(int bubble[],int n)
{
     
    int inc,inc1;
     for(inc=0;inc<n;inc++)
                 {
                    printf("%d",bubble[inc]);
                    }
    for(inc=0;inc<n;inc++)
    {
         for(inc1=(n-1);inc1>inc;inc1--)
         {
            if(bubble[inc1]<bubble[inc1-1])
            {
                 int temp;
                 temp = bubble[inc1];
                 bubble[inc1]=bubble[inc1-1];
                 bubble[inc1-1] = temp;
                 }
         }
}
                 for(inc=0;inc<n;inc++)
                 {
                    printf("%d",bubble[inc]);
                    }                       
    
    
    
}

 
int main(void)
{

    int a =1,n,bubble[n],inc;
/*    void change_it(int);*/
    printf("%d\n",a);
    printf("enter the value of n i.e the size of array\n");
    scanf("%d",&n);
    printf("Enter tihe values in the Array");
    for(inc=0;inc<n;inc++)
    {
            scanf("%d",&bubble[inc]);
            }
    change_it(a);
    bubblesort(bubble,n);
    printf("%d\n",a);
    getch();
    return 0;
    }

February 10th, 2013, 02:13 PM

salem

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> can't we allocate arraysize dynamically?

> int a =1,n,bubble[n],inc;
First of all, the value of n is garbage, so your array length is also garbage. The array length isn't revised automatically whenever you input a new value for n.

Second, variable length arrays such as this were introduced in C99. dev-c++ (which uses gcc, supports C99 (and did so as an extension prior to C99).

Visual studio does not support C99, and so it's a syntax error.

If you want something portable, then do this.

Code:

int *bubble;
...
    printf("enter the value of n i.e the size of array\n");
    scanf("%d",&n);
    bubble = malloc( n * sizeof(*bubble) );
...// do your thing
    free(bubble);

Comments on this post

Technovicez agrees!

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February 10th, 2013, 02:14 PM

dwise1_aol

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I don't see where you ever call malloc or calloc to allocate any array dynamically. Just how do you think that you're allocating an array dynamically?

I can't see how MinGW gcc (the compiler that Dev-C++ uses) would have compiled that. Unless it's one of those weird C99 things. MS Visual Studio doesn't support C99, because C99 mostly just tries to bring C up-to-date with C++ and Microsoft is investing in C++ and supports ANSI C (AKA "C89") which is what everybody uses.

Comments on this post

Technovicez agrees!

February 11th, 2013, 12:40 AM

Technovicez

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Thanks a Ton....

Sir U Specified that
[highlight]
"The array length isn't revised automatically whenever you input a new value for n."
[\highlight]
how to know about this aspect, i mean any resources to know when array is allocated memory whether is it is revised automatically .Not only this in general all datastructures.

February 11th, 2013, 01:49 AM

salem

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Quote:

Originally Posted by Technovicez

how to know about this aspect, i mean any resources to know when array is allocated memory whether is it is revised automatically .Not only this in general all datastructures.

1. Investigate realloc while you're reading about malloc.

2. Use C++ containers

Allocation of array size dynamically

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