Using pointers in Inverse polish calculator

[Sailors]

The code works well but I wish to represent the s[0], s[1], s[i], s[++i] using pointer notation and still have the code working. eg input 4 5 + , output 9 which correct

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

#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0' /* signal that a number was found */
#define MAXVAL 100 /* maximum depth of val stack */
int getop(char []);
void push(double);
double pop(void);
/* reverse Polish calculator */
main()
      {
    int type;
    double op2;
    double a, b,q;
    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;
    }
  }
  //getchar();
return 0;
}

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;
             }
        }
        
void ungetch(int);

int getop(char s[]){
 char *stp;/* I'm trying to use this pointer  for s[0], s[1], s[i], s[s++i] */ 
 stp = s;
         
       int i, c;
while ((s[0] = c = getchar()) == ' ' || c == '\t'); 
     s[1] = '\0';
     if (!isdigit(c) && c != '.')
     return c; 
     i = 0;
      if (isdigit(c)) 
     while ((isdigit(s[++i] = c = getchar())));
     if (c == '.') 
     while ((isdigit(s[++i] = c = getchar())));
     s[i] = '\0';
             
     if ( c != EOF)
     ungetch(c);
     return NUMBER;
}

[MacGyver]

http://cboard.cprogramming.com/showthread.php?t=92182

[Sailors]

I've tried all you suggested about the pointer in this code but it didn't work. I guess it will be better if you can try same and see if it wil work and tell me where the problem is

[MacGyver]

You were asked in the last topic to post your latest attempt.

[Sailors]

You were asked in the last topic to post your latest attempt.

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

#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0' /* signal that a number was found */
#define MAXVAL 100 /* maximum depth of val stack */
int getop(char []);
void push(double);
double pop(void);
/* reverse Polish calculator */
main()
      {
    int type;
    double op2;
    double a, b,q;
    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;
    }
  }
  //getchar();
return 0;
}

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;
             }
        }
        
void ungetch(int);

int getop(char s[]){
 char *stp;/* I'm trying to use this pointer  for s[0], s[1], s[i], s[s++i] */ 
 stp = s;
         
       int i, c;
while ((*(s) = c = getchar()) == ' ' || c == '\t'); 
     *(s+1) = '\0';
     if (!isdigit(*(s)) && c != '.')
     return *(s); 
     i = 0;
      if (isdigit(*(s))) 
     while ((isdigit(*(s+(++i)) = c = getchar())));
     if (*(s) == '.') 
     while ((isdigit(*(s+(++i)) = c = getchar())));
     *(s+i) = '\0';
             
     if ( *(s) != EOF)
     ungetch(c);
     return NUMBER;
}

[Sailors]

I've gotten it don't worry, thanks