#include <stdio.h>
#include <stdlib.h>
  
  int main()
  {  int *ps, *pr, *pt;
    char* str;
    int i;
    ps = (int *) malloc(4);
    pr = (int *) malloc(4);
    printf("ps is %p\n", ps);
    printf("pr is %p\n", pr);
    *ps = 5;
    printf("ps is %p *ps is %d\n",ps,*ps);
    printf("pr is %p *pr is %d\n",pr,*pr);   // *pr has not been initialized
    free (ps);
//   free (ps);           // Generates error
    free (pr);
    printf("\n");
  
    str= (char *) calloc(8,sizeof(char));
    ps = (int *) calloc(1,sizeof(int));
    pr = (int *) calloc(1,sizeof(int));
    pt = (int *) calloc(1,sizeof(int));
    printf("ps is %p\n", ps);
    printf("pr is %p\n", pr);
    printf("pt is %p\n", pt);
    printf("str is %p\n", str);
    *ps = 5;
    *pt = 7;
    for(i=0; i<8; i++)
       {str[i]='a';
       }
    printf("ps is %p *ps is %d\n",ps,*ps);
    printf("pr is %p *pr is %d\n",pr,*pr);
    printf("pt is %p *pt is %d\n",pt,*pt);
    for (i=0; i<8; i++)
        printf("-%c",str[i]);
    printf("\n");
    free (ps);
    free (pr);
    free (pt);
    free (str);
    printf("\n");
  
    str= (char *) calloc(8,sizeof(char));
    ps = (int *) calloc(1,sizeof(int));
    pr = (int *) calloc(1,sizeof(int));
    pt = (int *) calloc(1,sizeof(int));
    for(i=0; i<8; i++)
       {str[i]='f';
       }
    pr = 0;  // will cause segmentation fault later on
    printf("ps is %p\n", ps);
    printf("pr is %p\n", pr);
    printf("pt is %p\n", pt);
    printf("str is %p\n", str);
    *ps = 5;
    for(i=0; i<8; i++)
       str[i]='a';
    printf("ps is %p *ps is %d\n",ps,*ps);
    printf("pt is %p *pt is %d\n",pt,*pt);
    for (i=0; i<8; i++)
        printf("-%c",str[i]);
    printf("\n");
//    printf("pr is %p *pr is %d\n",pr,*pr); // Segmentation fault
    free (ps);
    free (pr);
    free (pt);
    free (str);
    printf("\n");
  
  }