/* * File: rpncalc.c * --------------- * This program simulates an electronic calculator that uses * reverse Polish notation, in which the operators com after * the operands to which they apply. */
#include <stdio.h>#include <ctype.h>#include "genlib.h"#include "simpio.h"#include "strlib.h"#include "stack.h"
/* Private function prototypes */
static void ApplyOperator(char op, stackADT operandStack);
static void HelpCommand(void);
static void ClearStack(stackADT operandStack);
static void DisplayStack(stackADT operandStack);
/* Main program */int main() {    stackADT operandStack;    string line;    char ch;
    printf("RPN Calculator Simulator (type H for help)\n");    operandStack = NewStack();    while (TRUE) {        printf("> ");        line = GetLine();
        ch = toupper(line[0]);        switch (ch) {            case 'Q':                exit(0);            case 'H':                HelpCommand();                break;            case 'C':                ClearStack(operandStack);                break;            case 'S':                DisplayStack(operandStack);                break;            default:                if (isdigit(ch)) {                    Push(operandStack, StringToReal(line));                } else {                    ApplyOperator(ch, operandStack);                }                break;
        }    }
    return 0;}
/* Private functions */
/* * Function: ApplyOperator * Usage: ApplyOperator(op, operandStack); * --------------------------------------- * This function applies the operator to the top two elements on * the operand stack. Because the elements on the stack are * popped in reverse order, the right operand is popped before * the left operand. */
static void ApplyOperator(char op, stackADT operandStack) {    double lhs, rhs, result;
    rhs = Pop(operandStack);    lhs = Pop(operandStack);    switch (op) {        case '+':            result = lhs + rhs;            break;        case '-':            result = lhs - rhs;            break;        case '*':            result = lhs * rhs;            break;        case '/':            result = lhs / rhs;            break;        default:            Error("Illegal operator %c", op);    }    printf("%g\n", result);    Push(operandStack, result);}
/* * Function: HelpCommand * Usage: HelpCommand(); * --------------------- * This function generate a help message for the user; */
static void HelpCommand(void) {    printf("Enter expression in Reverse Polish Notation, \n");    printf("in which operators follow the operands to which\n");    printf("they apply. Each line consists of a number, an\n");    printf("operator, or one of the following commands: \n");    printf("  Q -- Quit the program\n");    printf("  H -- Display this help message\n");    printf("  C -- Clear the calculator stack\n");    printf("  S -- Display all values in the stack\n");}

/* * Function: ClearStack * Usage: ClearStack(stack); * ------------------------- * This function clears the stack by popping elements until it is * empty. */static void ClearStack(stackADT stack) {    while (!StackIsEmpty(stack)) {        (void)Pop(stack);    }}
/* * Function: DisplayStack * Usage: DisplayStack(stack); * --------------------------- * This function displays the contents of a stack. */
static void DisplayStack(stackADT stack) {    int i, depth;
    printf("Stack: ");    depth = StackDepth(stack);    if (depth == 0) {        printf("empty\n");    } else {        for (i = depth - 1; i >= 0; i--) {            if (i < depth - 1) {                printf(", ");            }            printf("%g", GetStackElement(stack, i));        }    }}