C - Reverse Polish Calculator

雨点打透心脏的1/2处 2022-11-04 11:19 125阅读 0赞

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/*
     * A reverse Polish calculator
     *
     * ReversePolishCalculator.c - by FreeMan
     */
    
    #include <stdio.h>
    #include <stdlib.h> /* For atof() */
    
    #define MAXOP 100 /* Max size of operand or operator */
    #define NUMBER '0' /* Signal that a number was found */
    
    int GetOp(char[]);
    void Push(double);
    double Pop(void);
    
    /* Reverse Polish calculator */
    main()
    {
    	int type;
    	double op2;
    	char s[MAXOP];
    	while ((type = GetOp(s)) != EOF) {
    		switch (type) {
    		case NUMBER:
    			Push(atof(s));
    			break;
    		case '+':
    			Push(Pop() + Pop());
    			break;
    		case '*':
    			Push(Pop() * Pop());
    			break;
    		case '-':
    			op2 = Pop();
    			Push(Pop() - op2);
    			break;
    		case '/':
    			op2 = Pop();
    			if (op2 != 0.0)
    			{
    				Push(Pop() / op2);
    			}
    			else
    			{
    				printf("error: zero divisor\n");
    			}
    			break;
    		case '\n':
    			printf("\t%.8g\n", Pop());
    			break;
    		default:
    			printf("error: unknown command %s\n", s);
    			break;
    		}
    	}
    	return 0;
    }
    
    #define MAXVAL 100 /* Maximum depth of val stack */
    
    int sp = 0; /* Next free stack position */
    double val[MAXVAL]; /* Value stack */
    
    /* Push: Push f onto value stack */
    void Push(double f)
    {
    	if (sp < MAXVAL)
    	{
    		val[sp++] = f;
    	}
    	else
    	{
    		printf("error: stack full, can’t push %g\n", f);
    	}
    }
    
    /* Pop: Pop and return top value from stack */
    double Pop(void)
    {
    	if (sp > 0)
    	{
    		return val[--sp];
    	}
    	else
    	{
    		printf("error: stack empty\n");
    		return 0.0;
    	}
    }
    
    #include <ctype.h>
    
    int GetCh(void);
    void UngetCh(int);
    
    /* GetOp: Get next character or numeric operand */
    int GetOp(char s[])
    {
    	int i, c;
    	while ((s[0] = c = GetCh()) == ' ' || c == '\t')
    		;
    	s[1] = '\0';
    	if (!isdigit(c) && c != '.') /* Not a number */
    	{
    		return c;
    	}
    	i = 0;
    	if (isdigit(c)) /* Collect integer part */
    	{
    		while (isdigit(s[++i] = c = GetCh()))
    			;
    	}
    	if (c == '.') /* Collect fraction part */
    	{
    		while (isdigit(s[++i] = c = GetCh()))
    			;
    	}
    	s[i] = '\0';
    	if (c != EOF)
    	{
    		UngetCh(c);
    	}
    	return NUMBER;
    }
    
    #define BUFSIZE 100
    
    char buf[BUFSIZE]; /* Buffer for UngetCh */
    int bufp = 0; /* Next free position in buf */
    
    int GetCh(void) /* Get a (possibly pushed-back) character */
    {
    	return (bufp > 0) ? buf[--bufp] : getchar();
    }
    void UngetCh(int c) /* Push character back on input */
    {
    	if (bufp >= BUFSIZE)
    	{
    		printf("UngetCh: too many characters\n");
    	}
    	else
    	{
    		buf[bufp++] = c;
    	}
    }
    
    // Output:
    /*
    1 2 + 3 4 - * 5 6 + /
    		-0.27272727
    
    */

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