INTERVIEW QUESTIONS C ARRAYS IN C DETAILS

Question: Can the size of an array be declared at runtime?

Answer: No. In an array declaration, the size must be known at compile time. You can’t specify a size that’s known only at runtime. For example, if i is a variable, you can’t write code like this:

char array[i]; /* not valid C */

Some languages provide this latitude. C doesn’t. If it did, the stack would be more complicated, function calls would be more expensive, and programs would run a lot slower. If you know that you have an array but you won’t know until runtime how big it will be, declare a pointer to it and use malloc() or calloc() to allocate the array from the heap.

No. In an array declaration, the size must be known at compile time. You can’t specify a size that’s known only at runtime. For example, if i is a variable, you can’t write code like this:

char array[i]; /* not valid C */

Some languages provide this latitude. C doesn’t. If it did, the stack would be more complicated, function calls would be more expensive, and programs would run a lot slower. If you know that you have an array but you won’t know until runtime how big it will be, declare a pointer to it and use malloc() or calloc() to allocate the array from the heap. Source: CoolInterview.com

This is valid as per latest C standards. Try the following (I tried this on Linux, gcc version 4.1.2)

#include <stdio.h>

int my_fn(int size)
{
char s[size];

memset(s,0,size);
memset(s,'1',size-1);

printf("%s
",s);

return 0;
}

int main(int argc, char *argv[])
{
int arg=10;

if ( argc == 2 )
{
arg=atoi(argv[1]);
printf("New arg = %d
",arg);
}
my_fn(arg);

return 0;
}

Run ./a.out 5, ./a.out 15 etc Source: CoolInterview.com

Yes.
consider the piece of code shown below,

main()
{
int size;
printf("Enter array size");
scanf("%d",&size);
int array[size];
/* Remaining code
.
*/
}

Theoratically,this is true but this type of code is not implemented in real-time application.This type of code is poor programming practise but still the code works. Source: CoolInterview.com

In MSVC, you can't as suggested but in GNU C you can. For example, the code below is perfectly legitimate:

main(){
int size;
scanf("%d", &size);

int arr[size];

int i;
for(i=0; i<size; ++i){
arr[i] = i;
printf("%d ", arr[i]);
}
} Source: CoolInterview.com

size can be given at run time also...
ex-
int n;
scanf("%d",&n);
int a[n];

and it works successfully Source: CoolInterview.com

no,we cant give array size at runtime ...in subscript operator,there can be a integer or name of macro....there can not be anything else like constant and variable. Source: CoolInterview.com

Can an array be allocated mem at run time. No, never. All answers given have a common problem. See the question is can an array be defined without size and then allocated memory, that doesn't happen in any answers given.

void main()
{
int n;
scanf("%d",&n); // now give input
int a[n]; // which means array is given its size as 'n'. Now it is static
}
Then can u modify its size, no, impossible.
Try and understand pointer.

A pointer is defined without any size and can be allocated memory later and can also be modified later. That is dynamic. Source: CoolInterview.com

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