Question on array

This is a discussion on Question on array within the C Programming forums, part of the General Programming Boards category; Hi , I have question about array. The program below has a fix array(100). I want the size of the ...

  1. #1
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    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]);
      }
    }

  2. #2
    Epy
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    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;
    Last edited by Epy; 11-25-2009 at 09:02 AM. Reason: added some more notes

  3. #3
    Epy
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    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

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