【晨哥的C语言之旅】逆波兰表达式实现计算器功能

 

 

 

/*逆波兰表达式实现简单的计算器功能*/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define MAXOP  100   
#define NUMBER  '0'
#define MAXVAL 100
#define BUFSIZE 100

int getop(char []);
void push(double);
double pop(void);
int getch(void);
void ungetch(int);

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 '-':
                push(pop() + pop());
                break;
            case '/':
                op2 = pop();
                if (op2 != 0.0)
                    push(pop() /op2);
                else 
                    printf("error: zero divisor\n");
                break;
            default:
                printf("error: unknown command %s\n", s);

        }
    }
    return 0;
}


int sp = 0;
double val[MAXVAL];

void push(double f){
    if(sp < MAXVAL)
        val[sp++] = f;
    else
        printf("error: stack full, can't push %g\n", f);
}

double pop(void){
    if (sp > 0)
        return val[--sp];
    else{
        printf("error: stack empty\n");
        return 0.0;
    }
}

int getop(char s[]){
    int i, c;
    while((s[0] = c = getch()) == ' ' || c == '\t')
        ;
    s[1] = '\0';
    if (!isdigit(c) && c != '.')
        return c;
    i = 0;
    if(isdigit(c))
        while (isdigit(s[++i] = c = getch()))
            ;
    if(c == '.')
        while (isdigit(s[++i] = c = getch()))
            ;
    s[i] = '\0';
    if(c != EOF)
        ungetch(c);
    return NUMBER;
}

char buf[BUFSIZE];
int bufp = 0;

int getch(void){
    return (bufp > 0)? buf[--bufp] : getchar();
}

void ungetch(int c){
    if(bufp >= BUFSIZE)
        printf("ungetch: too many characters\n");
    else
        buf[bufp++] = c;
}