NB: Answer Question 1 and EITHER Question 2 OR Question 3. That is, you must answer Question 1, and one other question.

Question 1. (There are 4 parts to this question).

1.

a) Briefly explain the functions of the following UNIX commands. Do not explain what each option available to each command does, unless explicitly asked. For example:

wc -l : counts the number of lines entered from standard input

but

cd : change the current working directory to the default (HOME) directory

ls -la
csh
setenv EDITOR emacs
ps
grep path essay*
chmod go+rx *
nohup myprog >& myfile &


[10 marks]

b) The UNIX commands sort and grep are examples of filters. Explain what a filter is. What rules must be followed in order for a command or program to be eligible for use as a filter?

[15 marks]

c) What is a process? Explain the typical life cycle of a process in the UNIX environment, and describe the sorts of events that cause a process to change from one state to another.

[15 marks]

d) While running an interactive job a novice UNIX user pressed CTRL-Z. Then the UNIX command line prompt was displayed. What happened? What needs to be done to restart the job?

[10 marks]

2

a) Explain the difference between Call-by-Value and Call-by-Reference.

[5 marks]

b) Write a function is_member(char x, char *string) which returns 1 (one) if x occurs anywhere in the character array, string, and 0 otherwise. You must use pointers to traverse the array.

[10 marks]

c) Explain the use of the following constructs

(*p)++
(*string++)[0]
p->x


[12 marks]

d) Write a program in ANSI C which counts the number of characters, words and lines read from standard input. The program will print out the totals, but will not print out the input that the user has typed. Additionally, the program should print out the longest word that was typed in. If there is more than one word of the same maximum length, it is sufficient to print the first one only.

This example Input

This is an
example of the sorts of terminal
inputs that could be typed in


would produce this example Output

Chars = 74, words = 15, lines = 3
Longest word is terminal

[23 marks]

3

a) The following program contains 8 different errors. Find the errors, explaining why each is an error. The program takes integer input and checks it to ensure that it is valid. The code must be exactly 4 digits long, the first digit being in the range 1 - 9, other digits in the range 0 - 9. It then displays an appropriate message.

N.B. The program does not contain any logical errors. Only one of the functions does not contain at least one error.

You can mark the errors, and write the explanation, on the attached worksheet. Be sure to write your candidate number on the worksheet.

#include <stdio.h>
#include <ctype.h>

int getcode(void);
int checkcode(float); 
void print_error(char [], int);
void make_string(char [], char []);

main() /* control function */
{
	int code, c; 
	char e_string[10] = "         "; 

	if ((d = checkcode(getcode())) != 3) 
	{
		print_error(e_string, d);
	}
	else
		printf("Welcome...\n"); 
	
}

int getcode(void) /* obtain code */
{
	int code = 0;
	int c;
	
	while ((c = getchar()) != EOF && c != '\n') {
		if (! isdigit(c)) 
			return -1; /* non-digit keyed in */
		else {
			code = (code * 10) + (c - '0'); /* build up number */
	}
	
	/* after code keyed in, is it in range? */

	if (code > 9999 || code <= 999) 
		return -2; /* not in range */
	else
		return code;
}




int checkcode(float code) /* validate code */ 
{ 
	if (code < 0) 
	{
		return code;
	}
	
	return code % 13; 
}

/* original version of checkcode() commented out 

int checkcode(float code)  /* validates code */ 
{
	if (code <= 0)
		return code;
	else
		return code % 13;
}
*/

print_error(char e_string[], int e_type) /* print the message */
{
	char e_string[]; 
	char reason[50];

	e_string[] = "Error: ";

	switch (e_type) {
		case -1:
			make_string(e_string, "Warning: ");
			make_string(reason, "Code is not all numeric")
			break;
		case -2:
			make_string(reason, "Code is not right length");
			break;
		default:
			make_string(reason, "Invalid code entered");
			break;
	}
	
	printf("%s %s\n", e_string, reason); 
}

void make_string(char e_string[], char x[])
{
	int i;
	
	for (i = 0; x[i] != '\0'; i++)
		e_string[i] = x[i];
	e_string[i] = '\0';
}

[28 marks]

b) Write an ANSI C function called getstring that reads a line of input from the terminal, terminated by the end of file character or newline, and stores it in a character array called buffer, which you should declare. What result should getstring return, in order for it to be useful for functions that use it?

[12marks]

c) Describe the behaviour of the following C function fragment. (array[] is an integer array containing integers, i, c and d are declared as integers. i contains the number of array cells in array[]):

	
	c = d = 0;

	do {
		c += array[d++];
	} while (d < i);

What would the behaviour have been if the array subscript was coded ++d instead of d++ ?

[10 marks]