CS102 - Lesson 8

Makefiles, Pointers, Arrays

Instructor: Professor Hong

## Calculator - All in 1 File
							
						```
#include <stdio.h>
#include <stdlib.h> // for atof()

// K&R page 76-79

#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 != 0.0)
                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;
    }
}

int getch(void);
void ungetch(int);

// getop: get next operator or numeric operand

int getop(char s[])
{
    int i, c;

while ((s[0] = c = getch()) == ' ' || c == '\t')
        ;

s[1] = '\0';
    if (!isdigit(c) && c != '.')
        return c; // not a number
    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) charater
{
    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;
}							
						```

## Calculator in Multiple Files - main.c
						```
#include <stdio.h>
#include <stdlib.h>
#include <calc.h>

// K&R page 76-79

#define MAXOP   100 // max size of operand or operator

// reverse Polish calculator
int main()
{
    int type;
    double op2;
    char s[MAXOP];