Exercise 1-21. Write a program entab that replaces strings of blanks by the minimum number of tabs and blanks to achieve 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? Approach entab is …
Exercise 1-20. Write a program detab that replaces tabs in the input with the proper number of blanks to space to the next tab stop. Assume a fixed set of tab stops, say every n columns. Should n be a variable or a symbolic parameter? Approach The key insight is that a tab does not …
Radix Sort is a non-comparison sorting algorithm — it never compares two elements directly. Instead, it sorts by processing individual digits, one digit position at a time from least significant to most significant (LSD approach). This lets it sort integers in O(n) time for a fixed number of digits, breaking the O(n log n) lower …
Exercise 1-19. 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. Approach The core algorithm is the classic two-pointer swap: place one index at the start of the string (i = 0) and one at the end (j = …
Exercise 1-18. Write a program to remove trailing blanks and tabs from each line of input, and delete entirely blank lines. The challenge here is that you cannot know whether a blank or tab is “trailing” until you have seen everything that follows it on the same line. The solution splits the work into two …
Exercise 1-17. Write a program to print all input lines that are longer than 80 characters. Approach This exercise is a direct application of the getline / main pattern introduced in K&R Section 1.9 — but now with a filter condition added to main. The key insight is that getline already returns the line length, …