CS 1723, First Exam, Selected Answers, 30 Sept, 1998

PROBLEM 1:=============================================================
runner% cat exam1_3.c
#include <stdio.h>
#include <stdlib.h>
struct a_tag {
   char ch;
   int num;
};
void main(void)
{
   struct a_tag a[26];
   int i;
   for (i = 0; i < 26; i++) {
      a[i].ch = 'a' + i;
      a[i].num = i + 1;
   }
   for (i = 0; i < 26; i++)
      printf("Index: %2i, ch: %c, num: %2i\n",
         i, a[i].ch, a[i].num);
}
runner% cc -o exam1_3 exam1_3.c
runner% exam1_3
Index:  0, ch: a, num:  1
Index:  1, ch: b, num:  2
Index:  2, ch: c, num:  3
 ... (21 lines missing)
Index: 24, ch: y, num: 25
Index: 25, ch: z, num: 26

PROBLEM 3:=============================================================
runner% cat main.c
/* 
 * main.c 
 * simple command interpreter
 * commands: 'i' for insert, 'd' for delete
 */
#include <stdio.h>
#include "queue.h"

void main(void)
{
        char c;
        while (1) {
                c = getchar();
                switch (c) {
                case 'i': if (!full()) { 
                                c = getchar();
                                insert(c);
                                printf("Inserted: %c\n", c);
                        }
                        else
                                printf("No room\n");    
                        break;
                case 'd': if (!empty()) {
                                c = delete(); 
                                printf("Deleted: %c\n", c);
                        }
                        else
                                printf("Empty queue\n");
                        break;
                case 'q': exit(0);
                default: printf("Illegal command: %c\n", c);
                        break;
                }  /* end of case */
                while ((c = getchar()) != '\n') 
                        ;
        }
}
---------------------------------------------------------
runner% cat queue.h
/* 
 * queue.h -- queue header file
 */
typedef char Queuetype;
Queuetype delete(void);
void insert(Queuetype);
int empty(void);
int full(void);
---------------------------------------------------------
runner% cat queue.c
/* 
 * queue.c -- queue implementation
 */
#include <stdio.h>
#include "queue.h"
#define Q_SIZE 4  /* maximum queue size */
static Queuetype q[Q_SIZE];  /* actual queue */
static int fp = 0;  /* front pointer */
static int rp = 0;  /* rear pointer */
static int qs = 0;  /* size of queue */

Queuetype delete(void)
{
        if (!empty()) {
                qs--;
                fp = (fp + 1)%Q_SIZE;
                return q[fp];
        }
        else {
                printf("Underflow\n");
                return 0;
        }
}

void insert(Queuetype c)
{
        if (!full()) {
                qs++;
                rp = (rp + 1)%Q_SIZE;
                q[rp] = c;
        }
        else
                printf("Overflow\n");
}

int empty(void)
{
        return qs == 0;
}

int full(void)
{
        return qs == Q_SIZE;
}
---------------------------------------------------------
runner% queue
ia
Inserted: a
ib
Inserted: b
ic
Inserted: c
d
Deleted: a
d
Deleted: b
d
Deleted: c
q
runner% 

PROBLEM 4.=============================================================
runner% cat exam4.c
     #include <stdio.h>
     #include <stdlib.h>
     #include <string.h>
     void strcpy1(char *, char *);
     void main(void)
     {
        char s[] = "UTSA";
        char *t;
        t = (char *) malloc(strlen(s) + 1);
        strcpy1(t, s);
        printf("s:""%s"", t:""%s""\n", s, t);
        printf("  t[1],   char: %c\n", t[1]);
        printf("    *t,   char: %c\n", *t);
        printf(" &t[0], string: %s\n", &t[0]);
        printf("   t+2, string: %s\n", t+2);
        printf("*(t+2),   char: %c\n", *(t+2));
     }
     void strcpy1(char *a, char *b)
     {
        while (*a++ = *b++)
           ;
     }

runner% lint -m -u exam4.c

function returns value which is always ignored
    printf          
runner% cc -o exam4 exam4.c
runner% exam4
s:UTSA, t:UTSA
  t[1],   char: T
    *t,   char: U
 &t[0], string: UTSA
   t+2, string: SA
*(t+2),   char: S
runner%