Exercise 4-13. Write a recursive version of the function reverse(s), which reverses the string s in place. An iterative reverse uses two indices walking inward from both ends, swapping until they meet. The recursive version does the same with the call stack: each call receives left and right indices, swaps those two characters, then recurses …
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. K&R’s printd (Section 4.10) prints a number recursively: recurse on n/10 to print all leading digits first, then putchar(n%10 + ‘0’) on the way back up. itoa must …
Exercise 4-11. Modify getop so that it doesn’t need to use ungetch. Hint: use an internal static variable. In the original calculator, getop calls ungetch once: when it reads a non-digit character to terminate a number, it pushes that character back so the next call to getop will see it. The fix: instead of pushing …
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. The original calculator reads the input one character at a time via getch/ungetch. This exercise replaces that machinery with a line-buffer approach: read the whole line into a static …
Exercise 4-9. Our getch and ungetch do not handle a pushed-back EOF correctly. Decide what their properties should be if an EOF is pushed back, then implement your decision. The bug: K&R’s original implementation uses char buf[BUFSIZE]. When ungetch(EOF) is called, EOF (typically -1) is stored as char. On platforms where char is unsigned, -1 …
Exercise 4-8. Suppose that there will never be more than one character of pushback. Modify getch and ungetch accordingly. The original K&R implementation uses an array buf[BUFSIZE] and an index bufp to support multiple pushed-back characters. If only one character of pushback is ever needed, the array becomes unnecessary. A single static int buf suffices …