223: CS Data Structures.
Instructor: Jim Aspnes
Homework One
Due Friday, January 25th, 2002, at 5:00pm.
Get an account
Get an account on the Zoo. Instructions can be found on the Web in the CS 223 How To document, accessible off of the main Web page.
Send me email
Send me email! My address is [e-mail]. Send me an email message with your full name, residential college (or department, if you are a graduate student), and your Zoo login name. Include a brief greeting or question if you want to. Remember: it's important that you be able to read mail at the account that you send your message from; among other things, it's where I'll send your password for Grade-o-Matic.
Write a program
Your task is to write a program that translates an obscure numbering system back into the standard Arabic numbers we all know and love. Each number is represented as a sequence of phrases separated by whitespace, and each phrase consists of either one or two positive numbers, also separated by whitespace. In a two-number phrase X Y, X must be strictly less than Y, and the value of the phrase is the product X*Y. The value of a one-number phrase X is just X. To compute the value of a sequence, first we group it into phrases by starting at the left and grouping each number X with its successor Y provided X is less than Y and X is not already part of a phrase. We then compute the value of each phrase and add them up. Some examples: Original sequence 1 2 3 4 5 2 1000 3 100 2 10 6 1 1 1 1 1 1 1 1 10 2 50 6 Phrases, marked with () (1 2) (3 4) 5 (2 1000) (3 100) (2 10) 6 1 1 1 1 1 1 1 1 10 (2 50) 6 Value 19 2327 7 116
Your task is to write a program number.c that reads a sequence of numbers from stdin, terminated by end-of-file, computes the value of this sequence according to the rules described above, and writes the value stdout, to followed by a newline. Your program should tolerate trailing whitespace in its input (such as a newline at the end of the sequence of numbers). Your program does not need to produce sensible outputs for empty inputs or inputs that contain characters other than whitespace and positive numbers, but should terminate normally in such cases (this means no infinite loops, bus errors, or similar catastrophes). You may assume that no value exceeds 231 - 1. Submit your program with /c/cs223/bin/submit 1 number.c.
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Clarifications
How do I send input to my program on stdin? If you are running your program from a terminal, just type at it. To send end-of-file, hit control-D at the start of a line. You can also create a file with a test input and redirect stdin to point to that file using the shell's redirection syntax, e.g., by running a command like: ./myprogram < test-input-file. How can I parse numbers in my input? We recommend using scanf, e.g. scanf("%u", &number). You can test the return value of scanf to detect end-of-file. Should I expect more than one sequence per file? No. The picture in the assignment is a little bit misleading in this respect; you do not need to detect anything but end of file to find the end of a sequence. For example, the following text is a perfectly legitimate input, which should cause your program to print the value 51: 1 2 3 4 5 6 7 What about non-integers in the input? program only needs to handle integers. This would be an error. Your
Do I need to use an array to store the input? It is possible (and probably easier) to solve the problem without using an array. Is there any limit to how long the input can be? No.
CS 223 home page: http://zoo.cs.yale.edu/classes/cs223/ Fri 03 May 2002 23:06:32 EDT hw1.tyx Copyright c 1998-2002 by Jim Aspnes
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