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5 - Pointers and Arrays

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. [1]

My solution​

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Official solution​

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Exercise 5-2​

Write getfloat, the floating-point analog of getint. What type does getfloat return as its function value? [1]

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Official solution​

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Exercise 5-3​

Write 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. [1]

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Official solution​

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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. [1]

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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. [1]

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Official solution​

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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). [1]

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Official solution​

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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? [1]

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Exercise 5-8​

There is no error checking in day_of_year or month_day. Remedy this defect. [1]

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Exercise 5-9​

Rewrite the routines day_of_year and month_day with pointers instead of indexing. [1]

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Official solution​

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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). [1]

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Official solution​

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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. [1]

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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. [1]

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Official solution​

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Exercise 5-13​

Write the program tail, which prints the last n lines of its input. By default, n is 10, let us 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. [1]

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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. [1]

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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. [1]

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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. [1]

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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.) [1]

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Exercise 5-18​

Make del recover from input errors. [1]

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Exercise 5-19​

Modify undcl so that it does not add redundant parentheses to declarations. [1]

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Exercise 5-20​

Expand del to handle declarations with function argument types, qualifiers like const, and so on. [1]

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Official solution​

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