How do I create an array with undefined length? (In C) - c

Question

I'm trying to create a program which randomly decides how many cards you have, then randomly allocates a value to each of those cards.
I have managed to randomise the amount of cards, and I know how to randomise their values using an array and a for loop, but the problem is that this method only works when I manually choose a value for the number of elements in the array, but I want the number of elements to be the random amount of cards.
How do I go about this?
Here's my code so far to show what I mean. And yes, I'm aware the code probably could be done better but this is my first C assignment and I'm a complete beginner.
Thanks :)
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <windows.h>
int main(void)
{
system("cls"); /* Clears output to start */
srand(time(NULL)); /* Sets seed for random number generator */
int player1_amount = rand() %9 + 2; /*Generates random number for player 1's amount of cards */
int player2_amount = rand() %9 + 2; /*Generates random number for player 2's amount of cards */
int a = 1; /* For loop purposes */
while(a <= 1) /* While loop to print out each player's amount of cards once */
{
printf("Player 1 you have %d cards! \n", player1_amount);
Sleep(500);
printf("Player 2 you have %d cards! \n", player2_amount);
a++;
}
Sleep(1000); /* Delays for 1 second before printing card values */
int values[3]; /* Creates an array with 3 elements, but I want the number of elements to be player1_amount from above */
int b; /* Random variable for the loop */
int size = sizeof(values) / sizeof(values[0]); /* Gets length of array */
for (b = 0; b < size; b++) /* For loop randomises 3 values and then stops */
{
values[b] = rand() % 10 +1;
}
printf("Player 1 your cards are"); /* For loop to print out the values one after the other */
for(b = 0; b < size; b++)
{
printf(" %d, ", values[b]);
}
getch();
return 0;
}

Answer 1

I believe you will want to use malloc or calloc for that with a pointer.
int *values = (int *)calloc(player1_amount, sizeof(int));
Just make sure you free your allocation when done:
free(values);

Answer 2

C allows you to declare variable sized array. If you are not interested in using functions like malloc or calloc you can simply use variable to declare array as I've done here :
#include <stdio.h>
void main()
{
int x;
printf("\nEnter the value of x : ");
scanf("%d" , &x);
int array[x];
for(i = 0 ; i < x ; i++)
{
printf("Enter the element : ");
scanf("%d" , &array[i]);
}
for(i = 0 ; i < x ; i++)
{
printf("%d " , array[i]);
}
}
This program runs correctly without any error. So your problem is solved here itself without using malloc or calloc. But just make sure you declare your array after scanning or giving value to your variable which will represent the size of your array(here : x is the variable) and in your case I guess : player1_amount.
But still if you want to use malloc then here it goes :
#include <stdio.h>
#include <stdlib.h>
void main()
{
int x , i;
int * array;
printf("\nEnter the value of x : ");
scanf("%d" , &x);
array = (int *) malloc(x * sizeof(int));
for(i = 0 ; i < x ; i++)
{
printf("Enter the element : ");
scanf("%d" , &array[i]);
}
for(i = 0 ; i < x ; i++)
{
printf("%d " , array[i]);
}
}
Both the codes will give you same output.
A little explanation ...
Malloc will take input parameter as the amount of memory you wish to allocate to given variable(like 'array' in our case) in bytes and will output the pointer to that block of memory.
Since here we are working with integer array the return type is cast as : (int *), had it been a character array we would type cast it as : (char *).