# K & R C Chapter 5 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 5 of the book for easy reference.

Chapter 5: Pointers and Arrays

1. Exercise 5-1. As written, getint treats a + or – not followed by a digit as a valid representation of zero. Fix it to push such a character back on the input.
Solution to Exercise 5-1.
2. Exercise 5-2.Write getfloat , the floating-point analog of getint . What type does getfloat return as its function value?
Solution to Exercise 5-2.
3. Exercise 5-3.GWrite a pointer version of the function strcat that we showed in Chapter 2: strcat(s,t) copies the string t to the end of s .
Solution to Exercise 5-3.
4. Exercise 5-4. Write the function strend(s,t) , which returns 1 if the string t occurs at the end of the string s , and zero otherwise.
Solution to Exercise 5-4.
5. Exercise 5-5. Write versions of the library functions strncpy , strncat , and strncmp , which operate on at most the first n characters of their argument strings. For example, strncpy(s,t,n) copies at most n characters of t to s . Full descriptions are in Appendix B.
Solution to Exercise 5-5.
6. Exercise 5-6. Rewrite appropriate programs from earlier chapters and exercises with pointers instead of array indexing. Good possibilities include getline (Chapters 1 and 4), atoi , itoa , and their variants (Chapters 2, 3, and 4), reverse (Chapter 3), and strindex and getop (Chapter 4).
Solution to Exercise 5-6.
7. Exercise 5-7. Rewrite readlines to store lines in an array supplied by main , rather than calling alloc to maintain storage. How much faster is the program?
Solution to Exercise 5-7.
8. Exercise 5-8.There is no error-checking in day_of_year or month_day. Remedy this defect.
Solution to Exercise 5-8.
9. Exercise 5-9.Rewrite the routines day_of_year and month_day with pointers instead of indexing.
Solution to Exercise 5-9.
10. Exercise 5-10. Write the program expr , which evaluates a reverse Polish expression from the command line, where each operator or operand is a separate argument. For example, expr 2 3 4 + * evaluates 2 X (3+4).
Solution to Exercise 5-10.
11. Exercise 5-11. Modify the programs entab and detab (written as exercises in Chapter 1) to accept a list of tab stops as arguments. Use the default tab settings if there are no arguments.
Solution to Exercise 5-11.
12. Exercise 5-12. Extend entab and detab to accept the shorthand entab -m +n to mean tab stops every n columns, starting at column m . Choose convenient (for the user) default behavior.
Solution to Exercise 5-12.
13. Exercise 5-13. Write the program tail, which prints the last n lines of its input. By default, n is 10, say, but it can be changed by an optional argument, so that tail -n prints the last n lines. The program should behave rationally no matter how unreasonable the input or the value of n. Write the program so it makes the best use of available storage; lines should be stored as in the sorting program of Section 5.6, not in a two-dimensional array of fixed size.
Solution to Exercise 5-13.
14. Exercise 5-14. Modify the sort program to handle a -r flag, which indicates sorting in reverse (decreasing) order. Be sure that -r works with -n.
Solution to Exercise 5-14.
15. Exercise 5-15.Add the option -f to fold upper and lower case together, so that case distinctions are not made during sorting; for example, a and A compare equal.
Solution to Exercise 5-15.
16. Exercise 5-16.Add the -d (“directory order”) option, which makes comparisons only on letters, numbers and blanks. Make sure it works in conjunction with -f .
Solution to Exercise 5-16.
17. Exercise 5-17. Add a field-handling capability, so sorting may be done on fields within lines, each field sorted according to an independent set of options. (The index for this book was sorted with -df for the index category and -n for the page numbers.)
Solution to Exercise 5-10.
18. Exercise 5-18. Make dcl recover from input errors.
Solution to Exercise 5-18.
19. Exercise 5-19. Modify undcl so that it does not add redundant parentheses to declarations.
Solution to Exercise 5-19.
20. Exercise 5-20. Expand dcl to handle declarations with function argument types, qualifiers like const , and so on.
Solution to Exercise 5-20.
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