## Feb 7, 2012

### K & R C Programs Exercise 7-5.

K and R C, Solution to Exercise 7-5:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Rewrite the postfix calculator of chapter 4 to use scanf and/or sscanf to do the input number conversion.
Read more about C Programming Language .

```/***********************************************************
* You can use all the programs on  www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact info@c-program-example.com
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
*                      Happy Coding
***********************************************************/

#include<stdio.h>
#include<math.h>       /*for atof()*/
#define MAXTOP 100     /* max size of operand or operator  */
#define NUMBER  '0'    /* SIGNAL THAT A NUMBER WAS FOUND   */
#define MAXVAL 100
int gettop(char []);
void push(double);
double pop(void);
int sp = 0;          /* Next free stack position. */
double val[MAXVAL];

//reverse Polish calulator
int main(void)
{
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("\nError: Zero divissor\n");
break;
case '%':
op2 = pop();
if(op2)
push(fmod(pop(), op2));
else
printf("\nError: Division by zero!");
break;
case '\n':
printf("\t%.8g\n",pop());
break;
default:
printf("error: unknown command %s\n", s);
break;

}
}
return 0;
}

/* Getop: get next operator or numeric operand. */
int getop(char s[])
{

int i = 0;
int c;
int rc;
static char lastc[] = " ";
sscanf(lastc,"%c", &c);
lastc[0] = ' ';

/* Skip whitespace */
while((s[0] = c ) == ' ' || c == '\t')
if(scanf("%",&c) == EOF)
c = EOF;
s[1] = '\0';

/* Not a number but may contain a unary minus. */
if(!isdigit(c) && c != '.' )
return c;

if(isdigit(c))
do{
rc = scanf("%c",&c);
if(!isdigit(s[++i] = c))
break;
}while(rc != EOF)

if(c == '.')
do{
rc = scanf("%c",&c);
if(!isdigit(s[++i] = c))
break;
}while(rc != EOF)

s[i] = '\0';
if(rc != EOF)
lastc[0] = c;
return NUMBER;

}

/* push: push f onto stack. */
void push(double f)
{
if(sp < MAXVAL)
val[sp++] = f;
else
printf("\nError: 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("\nError: stack empty\n");
return 0.0;
}
}

```
```Read more c programs

C Basic
C Strings
K and R C Programs Exercise```
You can easily select the code by double clicking on the code area above.

To get regular updates on new C programs, you can

You can discuss these programs on our Facebook Page. Start a discussion right now,

our page!

Share this program with your Facebook friends now! by liking it

(you can send this program to your friend using this button)

Like to get updates right inside your feed reader? Grab our feed!

To browse more C Programs visit this link