C Programming Language

Exercises and examples from the book C Programming Language by Brian Kernighan and Dennis Ritchie.

This repository does not contain all solutions or examples, not does it guarantee any correctness. Use at own risk.

Organization

The examples and exercises are organized by the book chapters and sections.

Run example/exercice

To execute an example from top level:

make run CHAPTER=X EXAMPLE=X-Y

or to execute an exercise from top level:

make run CHAPTER=X EXERCISE=X-Y

Global clean

Clean all examples and exercises from top level:

make clean

---

Examples and Exercise Index

Chapter 1: A Tutorial Introduction

• Example1-1: Hello world.
• Example1-2: Fahrenheit to celcius convertion.
• Example1-3: Fahrenheit to celcius convertion, for loop version.
• Example1-4: Copy input to output.
• Example1-5: Copy input to output. 2nd version.
• Example1-6: Count characters in input. 1st version.
• Example1-7: Count characters in input. 2nd version.
• Example1-8: Count lines in input.
• Example1-9: Count lines, words and characters in input.
• Example1-10: Count digits, white space and other characters from input.
• Example1-11: Power functions.
• Example1-12: Print longest input line using character arrays.
• Example1-13: Print longest input line. Specialized version.
• Exercise1-1: Run the "Hello, world" program on your system. Experiment with leaving out parts of the program, to see what error messages you get.
• Exercise1-2: Experiment to find out what happens when printf's argument string contains \c, where c is some character not listed above.
• Exercise1-3: Modify the temperature conversion program to print a heading above the table.
• Exercise1-4: Write a program to print the corresponding Celsius to Fahrenheit table.
• Exercise1-5: Modify the temperature conversion program to print the table in reverse order, that is from 300 degrees to 0.
• Exercise1-6: Verify that the expression getchar() != EOF is 0 or 1.
• Exercise1-7: Write a program to print the value of EOF.
• Exercise1-8: Write a program to count blanks, tabs and newlines.
• Exercise1-9: Write a program to copy its input to its output, replacing each string of one or more blanks by a single blank.
• Exercise1-10: Write a program to copy its input to its output, replacing each tab by \t, each backspace by \b, and each backslash by \. This makes tabs and backspaces visible in an unambiguous way.
• Exercise1-11: How would you test the word count program? What kinds of input are most likely to uncover bugs if there are any?
• Exercise1-12: Write a program that prints its input one word per line.
• Exercise1-13: Write a program to print a histogram of the lengths of words in its input. It is easy to draw the ihstogram with the bars horizontal; a vertical orientation is more challenging.
• Exercise1-14: Write a program to print a histogram of the frequencies of different characters in its input.
• Exercise1-15: Rewrite the temperature conversion program of Section 1.2 to use a function for conversion.
• Exercise1-16: Revise the main routine of the longest line program so it will correctly print the length of arbitrarily long input lines, and as much as possible of the text.
• Exercise1-17: Write a program to print all input lines that are longer than 80 characters.
• Exercise1-18: Write a program to remove trailing blanks and tabs from each line of input, and to delete entirely blank lines.
• Exercise1-19: 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.
• Exercise1-20: Write a program detab that replaces tabs in the input with the proper number of blanks to space to the nest tab stop. Assum a fixed set of tab stops, say every n columns. Should n be a variable or a symbolic parameter?
• Exercise1-21: Write a program entab that replaces strings of blanks by the minimum number of tabs and blanks to acheive the same spacing. Use the same tab stops as for detab. When either a tab or a single blank would suffice to reach a tab stop, which should be given preference?
• Exercise1-22: Write a program to "fold" long input lines into two or more shorter lines after the last non-blank character that occurs before the n-th column of input. Make sure your program does something intelligent with very long lines, and if there are no blanks or tabs before the specified column.
• Exercise1-23: 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.
• Exercise1-24: Skipped

Chapter 2: Type, Operators and Expressions

• Example2-1: Compilation of all small examples throughout the chapter.
  • strlen implementation
  • enums
  • check for leap years
  • atoi
  • lower
  • pseudo random implementation
  • delete all instances of a char from a string
  • strcat, contatenate strings
  • get n bits from position p
  • count 1 bits in x integer
• Exercise2-1: Determine the ranges of various C types: char, short, int and long.
  • WIP: Also calculate ranges for float and double
• Exercise2-2: Write a for loop to read from terminal without using && or ||.
• Exercise2-3: Write a function htoi(s) which converts a string from hex to int.
• Exercise2-4: Write a function that deletes all chars in a string that match the characters in another string.
• Exercise2-5: Write a function that returns the first location where a character of a string appears on another one.
• Exercise2-6: Write a function that set the n bits from p in x according to bits from y.
• Exercise2-7: Write a function that inverts a range of bits from x.
• Exercise2-8: Write a function that returns x rotated by n bit positions.
• Exercise2-9: Write a faster version of bitcount.
• Exercise2-10: Write a version of lower function with conditional expressions.

Chapter 3: Control Flow

• Example3-1: Compilation of all small examples throughout the chapter.
  • binary search
  • count digits, white spaces and others using a switch-case statement
  • atoi: more general version
  • shell sort
  • reverse string in place
  • itoa
• Exercise3-1: Rewrite binsearch to use only one test inside the loop.
• Exercise3-2: Write a function that converts '\t' and '\n' into visible escape sequences, and a function that performs the opposite.
• Exercise3-3: Write a function that expands shorthand notations: a-z, 1-9, etc.
• Exercise3-4: Write a version o itoa that supports -(2^Wordsize-1).
• Exercise3-5: Write a version of itoa that supports different number basis.
• Exercise3-6: Write a version of itoa that has a minimum field width.

Chapter 4: Functions and Program Structure

• Example4-1: Program that prints each line that contains a matching string (grep-like)
• Example4-2: Compilation of all small examples throughout the chapter.
  • atof: convert strint to double
  • simple calculator
  • atoi implementation based on atof
• Example4-3: Reverse Polish calculator
• Example4-4: Reverse Polish calculator in multiple source files
• Example4-5: Recursive implementation of printd()
• Example4-6: Recursive quicksort implementation
• Exercise4-1: Write a function that prints the index of the rightmost occurence of t in s.
• Exercise4-2: Extend atof to handle scientific notation (123.45e-6)
• Exercise4-3: Extend example4-3 to calculate modulus
• Exercise4-4: Implement function to print stack top, duplicate stack top, swap top two stack itens and clear the stack. Without poping items
• Exercise4-5: Add access to math.h library functions (sin, cos, pow)
• Exercise4-6: Add commands for handling variables. Add a variable for most recently printed value
• Exercise4-7: Write a routine ungets(s) that will push back an entire string onto the input.
• Exercise4-8: Modify getch and ungetch to account for at most one character of pushback.
• Exercise4-9: Handle EOF push back in getch and ungetch
• Exercise4-10: getline to read an entire input line instead of getch and ungetch
• Exercise4-11: Modify getop so that it doesn't need to use ungetch.
• Exercise4-12: Write a recursive version of itoa() from printd().
• Exercise4-13: Write a recursive version of reverse(s), which reverses the string in place.
• Exercise4-14: Define a macro to swap two arguments of the same type.

Chapter 5: Pointers and Arrays

• Example5-1: getint function that returns integer from input stream.
• Example5-2: strlen v1 and v2.
• Example5-3: rudimentary storage allocator.
• Example5-4: strcpy array subscript version, pointer versions 1, 2 and 3.
• Example5-5: strcmp function array subscript and pointer versions.
• Example5-6: line sorting program (pointers to pointers).
• Example5-7: multidimensional arrays for date convertion.
• Example5-8: command line arguments: echo program versions 1 and 2.
• Example5-9: match pattern from command line.
• Example5-10: match pattern from command line with optional arguments.
• Example5-11: qsort with function pointers.
• Example5-12: dcl program. Convert C declaration to a word description. Recursive-descent parser.
• Example5-13: undcl program. Convert word description to C declaration.
• Exercise5-1: Fix getint to push back isolated + and - chars.
• Exercise5-2: Write getfloat based on getint.
• Exercise5-3: Write a pointer version of strcat().
• Exercise5-4: Write the function strend(s,t), checks for t at the end of s.
• Exercise5-5: Write a pointer version of strcpy(), strncat() and strncmp().
• Exercise5-6: [TODO] Rewrite pointer versions of previous functions.
• Exercise5-7: Rewrite readlinesto store lines in an array given by main.
• Exercise5-8: Add error checking to day_of_year and month_day.
• Exercise5-9: Rewrite day_of_year and month_day with pointers.
• Exercise5-10: Reverse Polish calculator from command line arguments.
• Exercise5-11: Skipped
• Exercise5-12: Skipped
• Exercise5-13: Write a simple version of tail program.
• Exercise5-14: Add reverse -r option to sort program.
• Exercise5-15: Add fold -f, so that upper and lower case letters compare equal.
• Exercise5-16: Skipped
• Exercise5-17: Skipped
• Exercise5-18: Skipped
• Exercise5-19: Skipped
• Exercise5-20: Skipped

Chapter 6: Structures

• Example6-1: compilation of simple initial examples.
• Example6-2: C keyword counting program.
• Example6-3: C keyword counting program with structure pointers.
• Example6-4: Count input works with binary trees.
• Example6-5: Table lookup with hash table.
• Example6-6: Unions.
• Exercise6-1: Skipped
• Exercise6-2: Skipped
• Exercise6-3: Read all different words and lines of appearence.
• Exercise6-4: Skipped
• Exercise6-5: Write a function undef that will remove a name and definition from the table maintained by lookup and install.
• Exercise6-6: Skipped

Chapter 7: Input and Output

• Example7-1: Convert input to lower case.
• Example7-2: Minimal printf with variable argument list.
• Example7-3: Rudimentary calculator with scanf().
• Example7-4: Read dates from stdin.
• Example7-5: cat program. Version 1.
• Example7-6: cat program. Version 2 with stderr.
• Example7-7: fgets(), fputs() and getline() implementations.
• Exercise7-1: Write a program that converts to lower or upper case, depending on argv[0].
• Exercise7-2: Skipped
• Exercise7-3: Skipped
• Exercise7-4: Skipped
• Exercise7-5: Skipped
• Exercise7-6: Write a program to compare two files, printing the first line where they differ.
• Exercise7-7: Skipped
• Exercise7-8: Skipped
• Exercise7-9: Skipped

Chapter 8: The UNIX System Interface

• Example8-1: Copy input to output. Low level implementation.
• Example8-2: getchar() implementations with low level functions.
• Example8-3: Simple cp program.
• Example8-4: Read any number of bytes from any position of a file.
• Example8-5: File pointer implementation from stdio.h.
• Example8-6: Listing directories.
• Example8-7: Storage allocator.
• Exercise8-1: Rewrite cat with low level functions.
• Exercise8-2: Skipped
• Exercise8-3: Skipped
• Exercise8-4: Skipped
• Exercise8-5: Skipped
• Exercise8-6: Skipped
• Exercise8-7: Skipped
• Exercise8-8: Skipped