Assignment: C Basics

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All Your Base Are Belong To Us

This assignment is part of the Student Built Xinu track for professors that are Teaching With Xinu. This particular assignment will help develop the student's proficiency for programming in C.

The Multi-Base Calculator

  • Write a calculator program that reads in expressions consisting of integers and the operators +, -, *, /, %, ^ (exponentiation), & (bitwise AND), | (bitwise OR), << (left shift), and >> (right shift), and prints the results when evaluated in simple left-to-right order.
  • Your calculator should understand positive integers in binary (starting with "0b",) octal, decimal, and hexadecimal, but all output will be in decimal (base-10).
  • You should use the getchar library function to read console input one character at a time. The use of any other library functions for input is not recommended at this time.


  • This project can seem deceptively complex, but is quite tractable if you first take the time to design suitable helper functions, and test those function thoroughly before moving on to the overall calculator. We encourage the disciplined practice of test-driven development.
  • The internal data representation of the calculator values can be assumed to be a signed int. You are not required to deal with overflow and underflow issues.
  • Parsing input is always tedious, particularly when the input is not rigidly constrained with rules like, "all operators must be surrounded by space on both sides," (which is NOT a constraint for this assignment). In lieu of a parser-generator, consider drawing simple state diagrams for how to recognize an integer in octal, or how to recognize an integer in hexadecimal. In many cases with input of this type, it is useful to be able to put back a character of input once you realize you have read too far. Useful C routines for implementing this kind of buffering include getch() and ungetch().
  • Consider various operational and parsing errors that can take place.
  • Devise test cases to discover the expected behavior, and do your best to match it precisely. Creativity will be valued in later assignments, but first one must master the tools.