C Programming Exercise Solutions

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C Programming Exercise Solutions

These are some of the exercises from different sections of the first chapter - CHAPTER 1: A Tutorial Introduction of the book C Programming Language (second edition) by Brian W. Kernighan and Dennis M. Ritchie.

The following are just eight of the exercises and solutions covering various topics of the introductory C programming.

1.1 Getting Started

Exercise 1-1

Run the "Hello, world" program on your system. Experiment with leaving out parts of the program to see what error messages you get.

Solution: ex_1_1.c

1.2 Variables and Arithmetic Expressions

Exercise

1-3 Modify the temperature conversion program to print a heading above the table.

Solution: ex_1_3.c

1.3 The For Statement

Exercise 1-5

Modify the temperature conversion program to print the table in reverse order, fom 300 degrees to 0.

Solution: ex_1_5.c

1.5 Character Input and Output

Exercise 1-8

Write a program to count blanks, tabs and newlines.

Solution: ex_1_8.c

1.6 Arrays

Exercise 1-13

Write a program to print a histogram of the lenghts of the words in its input. It is easy to draw a histogram with the bars horizontal; a vertical orientation is challenging.

Solution: ex_1_13.c

1.7 Functions

Exercise 1-15

Rewrite the temperature conversion program of Section 1.2 to use a function for conversion.

Solution: ex_1_15.c

1.9 Character Arrays

Exercise 1-19

Write a function reverse(s) that reverses the character string s. Use it to write a program that reverses its input a line at a time.

Solution: ex_1_19.c

1.10 External Variables and Scope

Exercise 1-23

Write a program to remove all comments from a C program. Don't forget to handle quoted strings and character constants properly. C comments do not nest.

Solution: ex_1_23.c

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C Programming Exercise Solutions

C Programming Exercise Solutions

ex_1_1.c

#include <stdio.h>

/* The Hello world program */
int main() 
{ 
	printf("Hello World!\n");
}

ex_1_13.c

#include <stdio.h>

/* Program to print a histogram for the input length of words.
   The histogram has horizontal bars. */
int main() 
{ 
	int c;

	while ((c = getchar()) != EOF)
		if (c != ' ' && c != '\n')
			printf("[]"); /* the histogram bar is made of these characters */
		else 
			printf("\n");
}

ex_1_15.c

#include <stdio.h>

#define	LOWER	0
#define	UPPER	300
#define	STEP	20

float convert(int fahr);

/* Fahrenheit to celsius conversion - using a function */
int main() 
{ 
	int fahr;

	printf(" Fahr\tCelsius\n");
	printf("================\n");
	for (fahr = LOWER; fahr <= UPPER; fahr = fahr + STEP)
		printf("%3d\t%6.1f\n", fahr, convert(fahr));
	return 0;
}

/* convert: converts fahrenheit to celsius for given fahr, returns the celsius */
float convert(int fahr) {
	return (5.0 / 9.0) * (fahr - 32.0);
}

ex_1_19.c

#include <stdio.h>

#define MAX_LINE_LEN	1000 /* Assume each line is limited to this length */

int get_line(char line[], int maxline);
void reverse(char s[]);

/* Program that reverses its input a line at a time.
   Uses a function reverse(s) that reverses the character string s. */
int main()
{
	char line[MAX_LINE_LEN];

	while((get_line(line, MAX_LINE_LEN)) > 0) {
		reverse(line);
		printf("%s\n", line);
	}

	return 0;
}

/* get_line: read a line into s, return length */
int get_line(char s[], int lim)
{
	int c, i;

	for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
		s[i] = c;
	if (c == '\n') {
		s[i] = c;
		++i;
	}
	s[i] = '\0';

	return i;
}

/* length: returns the length of string s */
int length(char s[]) 
{
	int i;

	i = 0;
	while (s[i] != '\0')
		++i;
	return i;
}

/* copy: copy from into to; assume to is big enough */
void copy(char to[], char from[])
{
	int i;

	i = 0;
	while ((to[i] = from[i]) != '\0')
		++i;
}

/* reverse: reverses the input string */
void reverse(char s1[])
{
	int i, j, len;

	len = length(s1); /* get length of the string */

	/* make copy of the original string */
	char s2[len];
	copy(s2, s1);

	/* make a reverse of the original string */
	j = 0;
	for (i = len-1; i >= 0; --i, ++j)
		s1[j] = s2[i];
}

ex_1_23.c

#include <stdio.h>

#define MAX_LINE_LEN	200	/* assume lines are limited to this length */
#define ON		1
#define OFF		0
#define ASTERIX		'*'
#define SLASH		'/'

int get_line(char line[], int maxline);
int get_ix(char s[], int lim, int comment_flag);
void remove_comments(int start_ix, char line[]);
void replace_comments(int start_ix, int end_ix, char line[], int len);

/* 
   Program to remove all comments in a C program.
   Assume
	- there can be single comment in a line (can have a single starting and/or ending)
	- comments can be leading or trailing only
	- a comment can span single or multiple lines
	- comments are syntactically correct, i.e., no nested comments
*/

int main()
{
	int len, start, start_ix, end_ix;
	char line[MAX_LINE_LEN], line_2[MAX_LINE_LEN];

	start = OFF;

	while((len = get_line(line, MAX_LINE_LEN)) > 0) {

		start_ix = get_ix(line, len, ON);
		end_ix = get_ix(line, len, OFF);

		if (start_ix >=0) {
			start = OFF;
			if (start_ix > 0) {
				remove_comments(start_ix, line);
				start = (end_ix >= 0) ? OFF : ON; /* comment can continue to next line */
			}
			else {
				if (end_ix >= 0 && end_ix < len-3) {
					/* leading comment (can be followed by code) */
					replace_comments(start_ix, end_ix, line, len);
				}
				else {
					/* comment starts and ends or continues */
					start = (end_ix == -1) ? ON : OFF;
				}
			}
		}
		else if (start == ON) {	/* comment started on previuos line */
			if (end_ix >= 0) {
				/* comment ends on this line */
				start = OFF; 
				if (end_ix < len-3) {
					replace_comments(start_ix, end_ix, line, len);
				}
			}
			/* else, comment continues on to next line */
		}
		else	
			printf("%s", line); /* code without any comments */
	}

	return 0;
}


/* replace_comments: replace comments with spaces (or tabs).
   this is used for leading comments only */
void replace_comments(int start_ix, int end_ix, char line[], int len)
{
	int i;

	for (i = 0; i < len; ++i) {
		if (i >= start_ix && i <= end_ix+1)
			line[i] = (line[i] == '\t') ? '\t' : ' ';
	}

	printf("%s", line);
}


/* remove_comments: removes the comment from the line */
void remove_comments(int start_ix, char line[])
{
	int new_len, i;

	new_len = start_ix;
	char new_line[new_len + 2];  /* add \n \0 in the end */

	for (i = 0; i < new_len; ++i)
		new_line[i] = line[i];

	new_line[i] = '\n';
	++i;
	new_line[i] = '\0';
	printf("%s", new_line);
}


/* get_ix: find if the line contains comment start or comment end; 
   return its index, else -1 */
int get_ix(char line[], int len, int flag)
{
	int c, i, comment;
	char first, last;	/* first and second charcters of starting or ending of a comment */

	if (flag == ON) {
		first = SLASH;
		last = ASTERIX;
	}
	else {
		first = ASTERIX;
		last = SLASH;
	}

	comment = OFF;

	for (i = 0; i < len; ++i) {
		c = line[i];
		if (c == first)
			comment = ON;
		else if (comment == ON && c == last)
			return --i;
		else
			comment = OFF;
	}
	return -1;
}


/* get_line: read a line into s, return its length */
int get_line(char s[], int lim)
{
	int c, i;

	for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
		s[i] = c;
	if (c == '\n') {
		s[i] = c;
		++i;
	}
	s[i] = '\0';

	return i;
}

ex_1_3.c

#include <stdio.h>

/* Program to convert fahrenheit to celsius and print - 
   for the fahrenheit 0 to 300 in steps of 20 */
int main() 
{ 
	int upper, lower, step;
	float fahr, celsius;

	lower = 0;
	upper = 300;
	step = 20;

	fahr = lower;
	printf(" Fahrenheit Celsius\n");
	printf("---------------------\n");
	while (fahr <= upper) {
		celsius = (5.0 / 9.0) * (fahr - 32) ;
		printf("   %3.0f      %6.1f\n", fahr, celsius);
		fahr = fahr + step;
	}
}

ex_1_5.c

#include <stdio.h>

/* Fahrenheit to celsius table - prints in reverse,
   for the fahrenheit 300 to 0 in steps of 20 */
int main()
{ 
	int fahr;

	printf("Fahrenheit\tCelsius\n");
	for (fahr = 300; fahr >= 0; fahr = fahr - 20)
		printf(" %3d\t\t%6.1f\n", fahr, (5.0 / 9.0) * (fahr - 32));
}

ex_1_8.c

#include <stdio.h>

/* Program to count tabs, blanks and newlines in the input */
int main() 
{ 
	int c, tb, bl, nl;

	nl = 0;
	bl = 0;
	tb = 0;
	while ((c = getchar()) != EOF)
		if (c == '\n')
			++nl;
		else if (c == '\t')
			++tb;
		else if (c == ' ')
			++bl;
	printf("Tab, blank and newline counts are %d %d %d\n", tb, bl, nl);
}