* Dynamic Memory Allocation
  * idea: useful to request memory as the program runs.
  * example: ask the user for the number of elements
             in an array

    int main()
    {
        int *values;
        int n;

        printf("Enter number of elements: ");
        scanf("%d", &n);
        //Use "calloc" to request memory:
        values = (int *) calloc (n, sizeof(int));
        //Now we can treat "values" like an ordinary array!
        values[0] = 1;
        ....
        //Use "free" to "release" memory:
        free(values);
    }

    Notes on calloc:
    * returns a pointer to an array of "chunks" of memory
    * 2nd arg = size of each chunk
    * 1st arg = # of elements (chunks) in the array
    * calloc returns a "generic pointer", so you need
      to "cast it" to a pointer of the appropriate type. 
    Notes on free:
    * "releases" the array that the pointer points to
 
  * Example 2: an array of structures
 
    #include<stdio.h>
    #include<string.h>

    typedef struct {
        char title[50];
        char artist[50];
        int rating;
    } CD;

    int main()
    {
        CD *cdlist;
        int n,i;

        printf("Enter number of elements: ");
        scanf("%d", &n);
        cdlist = (CD *) calloc (n, sizeof(CD));
        for (i = 0; i < n; i++) {
            strcpy(cdlist[i].title,"unknown");
            strcpy(cdlist[i].artist,"unknown");
            cdlist[i].rating = 0;
        }
        ....
        free (cdlist);
        return 0;
    }
       
  * Example 3: copying a string to another string

    1 #include <stdio.h>
    2 #include <string.h>

    3 int main()
    4 {
    5    char name1[] = "Sarah";
    6    char *name2;
    7    int n;

    8    n = strlen(name1);
    9    name2 = ( char * ) calloc ( n+1, sizeof(char) );
    10   strcpy(name2, name1);
    11   printf("%s\n", name1);
    12   printf("%s\n", name2);
    13   return 0;
    14 } 

     * Example 4: An Array of Pointers

     1 #include <stdio.h>
     2 #include <stdlib.h>
     3 #include <string.h>
 
     4 int main (void)
     5 {
     6    char s[50];
     7    char *names[100]; //names is an array of pointers to char
     8    int i,n,l;
 
     9    printf("enter number of names: ");
     10   scanf("%d", &n);
     11   for (i = 0; i < n; i++) {
     12      printf("enter name: ");
     13      scanf("%s", s);
     14      l = strlen(s);
     15      names[i] = (char *) calloc (l+1, sizeof(char));
     16      strcpy(names[i], s);
     17   }
     18   for (i = 0; i < n; i++)
     19      printf("%s\n", names[i]);
     20   for (i = 0; i < n; i++)
     21      free(names[i]);
     22   return 0;
     23 }

     * Example 5: Sorting An Array of Pointers

     1 #include <stdio.h>
     2 #include <stdlib.h>
     3 #include <string.h>

     4 void sort(char *list[], int n)
 
     5 int main (void)
     6 {
     7    char s[50];
     8    char *names[100];
     9    int i,n,l;
 
     10   printf("enter number of names: ");
     11   scanf("%d", &n);
     12   for (i = 0; i < n; i++) {
     13      printf("enter name: ");
     14      scanf("%s", s);
     15      l = strlen(s);
     16      names[i] = (char *) calloc (l+1, sizeof(char));
     17      strcpy(names[i], s);
     18   }
     19   sort(names,n);
     20   for (i = 0; i < n; i++)
     21      printf("%s\n", names[i]);
     22   for (i = 0; i < n; i++)
     23      free(names[i]);
     24   return 0;
     25 }

     26 void sort(char *list[], int n)
     27 {
     28     int pass, i;
     29     char *temp;
            
     30     for (pass = 0; pass < n-1; pass++)
     31         for (i = 0; i < n-1; i++ )
     32             if ( strcmp(list[i],list[i+1]) > 0 ) {
     33                  temp = list[i];
     34                  list[i] = list[i+1];
     35                  list[i+1] = temp;
     36              }
     37 }
     * Example 6: Sorting A 2-D Array

     1 #include <stdio.h>
     2 #include <stdlib.h>
     3 #include <string.h>

     4 void sort(char list[][50], int n)
 
     5 int main (void)
     6 {
     7    char s[50];
     8    char names[100][50];
     9    int i,n,l;
 
     10   printf("enter number of names: ");
     11   scanf("%d", &n);
     12   for (i = 0; i < n; i++) {
     13      printf("enter name: ");
     14      scanf("%s", s);
     15      strcpy(names[i],s);
     16   }
     17   sort(names,n);
     18   for (i = 0; i < n; i++)
     19      printf("%s\n", names[i]);
     20   return 0;
     21 }

     22 void sort(char list[][50], int n)
     23 {
     24     int pass, i;
     25     char temp[50];
            
     26     for (pass = 0; pass < n-1; pass++)
     27         for (i = 0; i < n-1; i++ )
     28            if ( strcmp(list[i],list[i+1]) > 0 ) {
     29                  strcpy(temp,list[i]);
     30                  strcpy(list[i],list[i+1]);
     31                  strcpy(list[i+1], temp);
     32            } 
     33 }