K&R C Chapter 2 Exercise Solutions — Types, Operators, and Expressions

Chapter 2: Types, Operators, and Expressions covers C’s type system and operators in depth. The exercises focus on bitwise manipulation — rotating bits, setting and clearing fields, counting set bits — and type-conversion edge cases. Exercise 2-9 (x &= (x-1) deletes the rightmost 1-bit) is a classic bit-manipulation trick worth memorising.

These are worked solutions to all 10 exercises. Each solution compiles cleanly with gcc -ansi -Wall.

Book: The C Programming Language, 2nd Ed — Kernighan & Ritchie  |  All chapters index

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Exercises

1. Exercise 2-1. Write a program to determine the ranges of char, short, int, and long variables, both signed and unsigned, by printing appropriate values from standard headers and by direct computation.

   Solution to Exercise 2-1

2. Exercise 2-2. Write a loop equivalent to the for loop above without using && or ||.

   Solution to Exercise 2-2

3. Exercise 2-3. Write the function htoi(s), which converts a string of hexadecimal digits (including an optional 0x or 0X) into its equivalent integer value. The allowable digits are 0 through 9, a through f, and A through F.

   Solution to Exercise 2-3

4. Exercise 2-4. Write an alternate version of squeeze(s1,s2) that deletes each character in s1 that matches any character in the string s2.

   Solution to Exercise 2-4

5. Exercise 2-5. Write the function any(s1,s2), which returns the first location in the string s1 where any character from the string s2 occurs, or -1 if s1 contains no characters from s2.

   Solution to Exercise 2-5

6. Exercise 2-6. Write a function setbits(x,p,n,y) that returns x with the n bits that begin at position p set to the rightmost n bits of y, leaving the other bits unchanged.

   Solution to Exercise 2-6

7. Exercise 2-7. Write a function invert(x,p,n) that returns x with the n bits that begin at position p inverted (i.e., 1 changed into 0 and vice versa), leaving the others unchanged.

   Solution to Exercise 2-7

8. Exercise 2-8. Write a function rightrot(x,n) that returns the value of the integer x rotated to the right by n bit positions.

   Solution to Exercise 2-8

9. Exercise 2-9. In a two’s complement number system, x &= (x-1) deletes the rightmost 1-bit in x. Explain why. Use this observation to write a faster version of bitcount.

   Solution to Exercise 2-9

10. Exercise 2-10. Rewrite the function lower, which converts upper case letters to lower case, with a conditional expression instead of if-else.

    Solution to Exercise 2-10

See also: K&R C — All Chapters Index | Complete C Programs List