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R.3  A Fancy Calculator

A Fancy Calculator

This Fancy Calculator showcases SheerPower’s powerful eval() function, which evaluates *all valid SheerPower expressions*. It handles arithmetic (e.g., 2+3), variables, built-in functions (like sin() or len()), logical operators (e.g., and, or), and string operations—everything SheerPower supports as an expression. Note: It does not execute arbitrary code like loops or statements, ensuring security. The code is below, with a detailed explanation. Try it out!

// Fancy Calculator in SheerPower print 'Calculator' print 'Enter any SheerPower expression (e.g., 2+3, sin(45), or "hello " + "world") to evaluate.' print 'Type Q to quit' // Define example variables for use in expressions x = 10 y = 5 name$ = "SheerPower" do line input prompt '>> ': expr$ lc_expr$ = lcase$(expr$) if lc_expr$ = 'q' then exit do when exception in print eval(expr$) // Evaluates any SheerPower // expression use print extext$;' for '; expr$ end when loop print 'done' stop

Program Explanation:

1. Introduction:

The program prints a welcome message and instructions, noting that *any SheerPower expression* can be evaluated. Variables x, y, and name$ are predefined for use in expressions.

2. Input Loop:

A loop prompts the user with >> to enter an expression, stored in expr$. Typing 'Q' (case-insensitive) exits.

3. Expression Evaluation:

The eval() function evaluates any valid SheerPower expression from expr$. Examples include:

  • Arithmetic: 2 + 3 → 5
  • Variables: x * y → 50 (using x=10, y=5)
  • Functions: sin(45) → approx. 0.707
  • Strings: name$ + " rocks" → SheerPower rocks
  • Logic: x > 5 and y < 10 → 1 (true)
It does not support statements like loops or assignments for security reasons.

4. Error Handling:

If an invalid expression is entered (e.g., 5/0 or for i = 1 to 10), the when exception in block catches it and prints the error via extext$.

5. End of Program:

Upon quitting, it prints "done" and stops.

Note: eval() processes *all SheerPower expressions*—math, strings, logic, and functions like sqrt(x) or len(name$). It won’t run full code blocks (e.g., print "hi"), keeping it secure and focused on expression evaluation.
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