Question on array

Hi ,

I have question about array. The program below has a fix array(100). I want the size of
the array to be determined by the user. How to write the code ?

The function "input_number" ask user to enter the size of the array. And i would like to allocate the entered value to be the size of the array. This way, user can enter more than 100 and my program will not crash.

Code:

---

#include<stdio.h>

int n, decimal;
int i, j, tmp;
int number[100];


input_number()
{
 int ch;
 
 printf("Enter how many element to store in array: ");
        decimal = 0;
            ch = getchar();
 
  while(ch != '\n')
    {
        if('0' <= ch && ch <= '9')
            {
                    decimal = decimal * 10;
                decimal = decimal + (ch - '0');
            }
         
          ch = getchar();
    }
       
}


input_array()
{
 int array;

 for(i=0;i<decimal;i++)
  {
  printf("Enter array %d: ",i+1);
 
        array = 0;
            ch = getchar();
 
  while(ch != '\n')
    {
        if('0' <= ch && ch <= '9')
            {
                    array = array * 10;
                array = array + (ch - '0');
        }
         
          ch = getchar();
    }

  number[i]=array;
  }
}
 



main()
{
 
 
 input_number();
 input_array();
 
 n=decimal;
 //print the unsorted numbers
 printf("\nUnsorted number : ");
 for(i=0;i<n;i++)
  {
  printf("%d, ",number[i]);
  }
 
  printf("\n");
 
 for(i=0;i<n-1;i++)
  {
  for(j=0;j<n-i-1;j++)
    {
        if(number[j]>number[j+1])
          {
          tmp = number[j];
          number[j] = number[j+1];
          number[j+1] = tmp;
          }
        }
  }
 
 //print the sorted numbers
 printf("Sorted number  : ");
 for(i=0;i<n;i++)
  {
  printf("%d, ",number[i]);
  }
}

---

If you're going to use C99, you can just use variable length arrays which are very straightforward:

Code:

---

int arraylength = 502;
int array[arraylength];

---

Otherwise, let me introduce malloc():

Code:

---

int arraylength = 502;
int *array;

/* allocate memory for arraylength number of integers
    size_t is the appropriate type for malloc and the type of sizeof()
    you do not need to cast malloc as an int type, this is unnecessary in ISO C
    see http://www.cprogramming.com/faq/cgi-bin/smartfaq.cgi?answer=1047673478&id=1043284351
*/
array = malloc((size_t)arraylength * sizeof(int));

if (!array)
{
    printf("\nMalloc failed!");
    exit(EXIT_FAILURE);
}

/* do stuff */

/* free up the memory that was allocated, set the array pointer to NULL so nothing else can use that now freed up memory block */
free(array);
array = NULL;

---

Should've mentioned that this is part of the C standard library. Also, you can check out calloc() which does the same thing except it initializes that memory block to 0s. Its syntax is slightly different:

Code:

---

array = calloc((size_t)arraylength, sizeof(int));

---

malloc - C++ Reference
calloc - C++ Reference