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.
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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 .
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#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 divissorn");
break;
case '%':
op2 = pop();
if(op2)
push(fmod(pop(), op2));
else
printf("nError: Division by zero!");
break;
case 'n':
printf("t%.8gn",pop());
break;
default:
printf("error: unknown command %sn", 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] = ' ';
/* 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] = ' ';
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 %gn", f);
}
/*pop: pop and return top value from stack.*/
double pop(void)
{
if(sp > 0)
return val[--sp];
else
{
printf("nError: stack emptyn");
return 0.0;
}
}
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