CODEWITHSUNDEEP
c
Daniel
Daniel

Reputation: 318

Size of an Array by user

I want the user to decide the size of my array
Can i do it?
I tried: 

#define max 8  
int a[max];

But then, user cant change a constant
I tried:

int i, a[i];

But it gives an error
Help?

Upvotes: 0

Views: 161

Answers (4)

Sandeep Kumar
Sandeep Kumar

Reputation: 336

As mentioned in above malloc is best way as it won't depend on compiler. Also because realloc can be done when you find that u need to increase of decrease the size of array.

int size;
printf("What's the array size?\n");
scanf("%d", &size);
array = (int *)malloc(size * sizeof(*array));
.
. 
. 
.some stuff on array
array = (int *)realloc(array, 1024); // changing size of array according to user.

more details regarding realloc is here resizing buffer using realloc

Upvotes: 3

Paulo
Paulo

Reputation: 1498

For a clean solution, use malloc() function, instead of int array[size];

int size;
printf("What's the array size?\n");
scanf("%d", &size);
array=(int *) malloc(size*sizeof(int));

Upvotes: 2

PC Luddite
PC Luddite

Reputation: 6108

Assuming your compiler supports C99 and variable-length arrays, then the following code will work:

int size;
fputs("Array size? ", stdout);
scanf("%d", &size);
int array[size];

If your compiler does not, you'll have to use malloc.

int size;
int* array;
fputs("Array size? ", stdout);
scanf("%d", &size);
array = malloc(size * sizeof(*array));
/* do stuff with array */
free(array); /* don't forget to free() when finished */

Some implementations support alloca, which allocates on the stack like a variable-length array would, but this is non-standard.

Upvotes: 5

asdf
asdf

Reputation: 3067

You need to define the array after you ask the user for input.

int size;
printf("Please enter the size of the array");
scanf(" %d", &size);
int array[size];

Upvotes: 4

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