Exercise 7.5. Rewrite the postfix calculator of Chapter 4 to use scanf and/or sscanf to do the input and number conversion.

Exercise 7.5. Rewrite the postfix calculator of Chapter 4 to use scanf and/or sscanf to do the input and number conversion.



#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#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 */
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 '-':
                op2 = pop();
                push(pop() - op2);
                break;
            case '/':
                op2 = pop();
                if(op2 != 0)
                    push(pop() / op2);
                else
                    printf("error: zero devisior\n");
                break;
            case '%':
                op2 = pop();
                if(op2 != 0.0)
                    push(fmod(pop(), op2));
                else
                    printf("error: zero devisor\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

double val[MAXVAL]; //value stack
int sp = 0; //next free stack position

/* push: push f into 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>

/* getop: get next character ot numeric operand */
int getop(char s[])
{
    int i, c, rc;
    static char lastc[] = " ";
   
    c = lastc[0];
    lastc[0] = ' ';
    while((s[0] = c) == ' ' || c == '\t')
        if(scanf("%c", &c) == EOF)
            c = EOF;
    s[1] = '\0';
    if(!isdigit(c) && c != '.' && c != '-') // not a number
        return c;
    i = 0;
    if (c == '-')
    {
        scanf("%c", &c);
        rc = c;
        if(isdigit(c) || c == '.')
            s[++i] = c; //negative numbers
        else
            {
                if(rc != EOF)
                    lastc[0] = c;
                return '-';
            }
    }
    if(isdigit(c)) //collect integer part
        do
        {
            scanf("%c", &c);
            rc = c;
            if(!isdigit(s[++i] = c))
                break;
        } while(rc != EOF);
    if(c == '.') //collect fraction part
        do
        {
            scanf("%c", &c);
            rc = c;
            if(!isdigit(s[++i] = c))
                break;
        } while(rc != EOF);
    s[i] = '\0';
    if(rc != EOF)
        lastc[0] = c;
    return NUMBER;
}

Result: