CS 1723, Data Structures, Exam 2, Selected Answers
/* CS 1723, Exam 2, Examples with strings, Problem 1 */
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

int digits1(char *);
int digits2(char *);
void change1(char *);
void change2(char *);

void main(void)
{
   char *s = (char *)malloc(20);
   char *t = (char *)malloc(20);
   char *u = (char *)malloc(20);
   strcpy(s, "Test 1: 4/2/1997");
   printf("String #1:\"%s\", digits: %i, %i\n",
      s, digits1(s), digits2(s));
   strcpy(t, "Test 2: stuvwxyz");
   printf("String #2:\"%s\", digits: %i, %i\n",
      t, digits1(t), digits2(t));
   strcpy(u, "Test Three: None");
   printf("String #3:\"%s\", digits: %i, %i\n",
      u, digits1(u), digits2(u));
   change1(s);
   printf("Changed String #1:\"%s\"\n", s);
   change2(t);
   printf("Changed String #2:\"%s\"\n", t);
   printf("String #3:\"%s\"\n", u);
}
int digits1(char *s)
{
   int len = strlen(s);
   int j;
   int count = 0;
   for (j = 0; j < len; j++)
      if (isdigit(s[j]))
         count++;
   return count;
}
int digits2(char *s)
{
   int count = 0;
   while (*s != '\0') /* or while(*s) */
      if (isdigit(*s++))
         count++;
   return count;
}
void change1(char *s)
{
   strcpy(s, "Newstring");
}
void change2(char *s)
{
   strcpy(s, "A string too long for allocation");
}
runner% cc -o exam2_1 exam2_1.c
runner% exam2_1
String:"Test 1: 4/2/1997", digits: 7, 7
String:"Test 2: stuvwxyz", digits: 1, 1
String:"Test Three: None", digits: 0, 0
Changed String #1:"Newstring"
Changed String #2:"A string too long for allocation"
String #3:""
(NOTICE: String t is OK, but string u was trashed!)

/* Weeks program, used in Problem 2, Exam2 */
#include <stdio.h>

void main(void)
{
   char **p, **q;
   char *weeks[] = {"none", "Monday", "Tuesday",
      "Wednesday", "Thursday", "Friday",
      "Saturday", "Sunday", NULL};
   p = weeks;
   printf("Printing weeks[4]:        %s\n", weeks[4]        );
   printf("Printing weeks[2][4]:     %c\n", weeks[2][4]     );
   printf("Printing *(weeks + 3):    %s\n", *(weeks + 3)    );
   printf("Printing *p:              %s\n", *p              );
   printf("Printing **p:             %c\n", **p             );
   printf("Printing *(*(p + 1) + 4): %c\n", *(*(p + 1) + 4) );
   q = &weeks[2];
   printf("Printing *q:              %s\n", *q              );
   printf("Printing **q:             %c\n", **q             );
}
runner% cc -o exam2_2 exam2_2.c
runner% exam2_2
Printing weeks[4]:        Thursday
Printing weeks[2][4]:     d
Printing *(weeks + 3):    Wednesday
Printing *p:              none
Printing **p:             n
Printing *(*(p + 1) + 4): a
Printing *q:              Tuesday
Printing **q:             T
runner% 
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/* List program, used in Problem 3 on Exam2 */
#include <stdio.h>
#include <stdlib.h>

struct lnode {
        char ch;
        struct lnode *next;
};

struct lnode *insert(char c, struct lnode *p);
void printlist(struct lnode *);

void main(void)
{
        char c;
        struct lnode *list = NULL;
        while ((c = getchar()) != '\n')
                list = insert(c, list);
        printlist(list);
}
struct lnode *insert(char c, struct lnode *p)
{
        struct lnode *q = 
            (struct lnode *) malloc(sizeof(struct lnode));
        q -> ch = c;
        q -> next = p;
        return q;
}
void printlist(struct lnode *p)
{
        while (p != NULL) {
                printf("%c", p -> ch);
                p = p -> next;
        }
        printf("\n");
}
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runner% cc -o exam2_3 exam2_3.c
runner% exam2_3 
abcdefg
gfedcba
runner%