Calculator program that provides the operators +, -, * and / as well as modulus %, print last result ?, duplicate last result #, swap last two results ~ and clear stack (memory) !. . It uses the reverse Polish notation. Section 4.3 of The C Programming Language.
- Each operator follows its operands; an infix expression like (1-2) * (4+5) is entered as 1 2 - 4 5 + *
- Parentheses are not needed; the notation is unambigueis as long as we know how many oprands each operator expects.
- Impllementation: Each oprand is pushed onto a stack; when an operator arrives, the proper number of operands (two for binary operators) is popped, the operator is applied to them, and the result is pushed back onto the stack.
- For instance, in the example above, 1 and 2 are pushed, then replaced by their difference -1. Next, 4 and 5 are pushed and then replaced by their sum 9. The product of -1 and 9, which is -9, replaces them on the stack. The value on the top of the stack is popped and printed when the end of the input line is encounted.
while (next operator or operand is not end-of-file indicator)
if (number)
push it
else if (operand)
pop operands
do operation
push result
else if (newline)
pop and print tor of stack
else
error
