# K & R C Chapter 4 Exercise Solutions.

We have already provided solutions to all the exercises in the bookC Programming Language (2nd Edition) popularly known as K & R C book.

In this blog post I will give links to all the exercises from Chapter 4 of the book for easy reference.

Chapter 4: Functions and Program Structure
1. Exercise 4-1. Write the function strrindex(s,t) , which returns the position of the rightmost occurrence of t in s , or -1 if there is none.
Solution to Exercise 4-1.
1. Exercise 4-2.Extend atof to handle scientific notation of the form 123.45e-6 where a floating-point number may be followed by e or E and an optionally signed exponent.
Solution to Exercise 4-2.
1. Exercise 4-3.Given the basic framework, it’s straightforward to extend the calculator. Add the modulus ( % ) operator and provisions for negative numbers.
Solution to Exercise 4-3.
1. Exercise 4-4. Add commands to print the top element of the stack without popping, to duplicate it, and to swap the top two elements. Add a command to clear the stack.
Solution to Exercise 4-4.
1. Exercise 4-5. Add access to library functions like sin , exp , and pow . See <math.h> in Appendix B, Section 4.
Solution to Exercise 4-5.
1. Exercise 4-6. Add commands for handling variables. (It’s easy to provide twenty-six variables with single-letter names.) Add a variable for the most recently printed value.
Solution to Exercise 4-6.
2. Exercise 4-7. Write a routine ungets(s) that will push back an entire string onto the input. Should ungets know about buf and bufp , or should it just use ungetch ?
Solution to Exercise 4-7.
1. Exercise 4-8.Suppose that there will never be more than one character of pushback. Modify getch and ungetch accordingly.
Solution to Exercise 4-8.
1. Exercise 4-9.Our getch and ungetch do not handle a pushed-back EOF correctly. Decide what their properties ought to be if an EOF is pushed back, then implement your design
Solution to Exercise 4-9.
1. Exercise 4-10. An alternate organization uses getline to read an entire input line; this makes getch and ungetch unnecessary. Revise the calculator to use this approach.
Solution to Exercise 4-10.
1. Exercise 4-11. Modify getop so that it doesn’t need to use ungetch. Hint: use an internal static variable.
Solution to Exercise 4-11.
1. Exercise 4-12. Adapt the ideas of printd to write a recursive version of itoa ; that is, convert an integer into a string by calling a recursive routine.
Solution to Exercise 4-12.
1. Exercise 4-13. Write a recursive version of the function reverse(s) , which reverses the string s in place.
Solution to Exercise 4-13.
1. Exercise 4-14. Define a macro swap(t,x,y) that interchanges two arguments of type t . (Block structure will help.)
Solution to Exercise 4-14.
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