Thread: Reverse Polish Calcullator

I'm doing KnR exercise 4-6:

Add access to library functions like sin, exp and pow to the polish calculator.

but I'm having a buffer problem. I'm trying to enter an exponent inside a function I called power (because I think people should choose the power they want).

But I'm getting this:

Code:

 
  current value of the top of the stack: 4.000000000000000Enter a power: You Entered: 0 Inserted value: 1.000000000000000000

heh, that buffer problem.

I know I have to reset the buffer. I tried to reset the val[MAXVAL] unsuccessfully.

What do I have to reset ?

edit:
I tried to reset s (I thought I had to reset it because, after all, s is a char*)

Code:

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

#ifndef NUMBER 
 #define NUMBER '0' 
#endif 


#ifndef MAXOP 
 #define MAXOP 100 
#endif


#ifndef PERIOD 
 #define PERIOD '.'
#endif 


#ifndef MAXVAL 
 #define MAXVAL 100 
#endif 


#ifndef MAXBUF 
 #define MAXBUF 100 
#endif 


int bufp = 0; 
char buf[MAXBUF];


int sp = 0; 
double val[MAXVAL];


int getch(void); 
void ungetch(int);
int getop(char*);
double pop(void);
void push(double);
void peek(void);
void duplicate(void);
void swap(void);
void clear(void);
double power(double);
int isanumber(char* s);


int main(void) 
{ 
  int type; 
  char s[MAXOP]; 
  double op2; 
  
  while( (type = getop(s)) != EOF)
  { 
    switch(type) 
    { 
      case NUMBER: 
        push(atof(s));
        break;
      
      case '+': 
        push(pop() + pop());
        break;
      
      case '-': 
        op2 = pop();
        push(pop() - op2);
        break;              
        
      case '*': 
        push(pop() * pop());
        break;
      
      case '\n': 
        printf("Polish pop: \t%.8g\n", pop());
        break;
        
      case 'i':
        push(sin(pop()));
        break;
        
      case 'e': 
        push(exp(pop()));
        break;
        
      case 'o': 
        push(power(pop()));
        break;  
      
      case 'p': 
        peek();
        break;  
        
      case 'd': 
        duplicate();
        break;  
      
      case 'c': 
        clear();
        break;  
        
      case 's': 
        swap();
        break;  
      
      case '/': 
        op2 = pop();
        if(op2 > 0.0) 
          push(pop() / op2);
        else 
          printf("error: zero divisor\n");
        break;
       
       case '%': 
         op2 = pop();
         if(op2 > 0.0) 
           push(fmod(pop(), op2));
         else 
           printf("error: zero divisor\n");
         break;
        
        default: 
          printf("error: unknown command\n");              
        break;  
    }       
  }           
  return EXIT_SUCCESS;     
}       

int isanumber(char* s) 
{ 
   int i; 
   for(i = 0; s[i] != '\0'; i++) 
    if(isalpha(s[i]))
      break;


   if(s[i] != '\0')
      return 0;
   return 1;
}

void push(double f) 
{ 
   if(sp < MAXVAL) 
   {  
      val[sp++] = f;  
      printf("Inserted value: %f\n", val[sp - 1]);
   }   
   else 
     printf("push: stack full, can't push %g\n", f);             
}


double power(double f) 
{ 
   char strnum[MAXVAL];
   int pw = 0;
   
   do  {
     printf("Enter a power: ");
     fgets(strnum, sizeof(strnum), stdin);    
   }while(!isanumber(strnum));
   
   pw = atoi(strnum);
   printf("You entered: %d", pw);
   
   return pow(f,pw); 
}     


void duplicate(void) 
{ 
   if(sp < MAXVAL) 
   { 
     val[sp++] = pop();  
   }
   else         
     printf("duplicate: stack full, can't push %f\n", pop()); 
}  


void swap(void) 
{ 
   double temp;
   
   if(sp > 0)
   {  
     temp = val[sp];
     val[sp] = val[sp - 1];
     val[sp - 1] = temp;    
   }
   else { 
     printf("swap: at least, two values have to be inserted for swapping.\n");
   }          
}


void clear(void) 
{ 
   int i;
   for(i = 0; i < MAXVAL; i++)
     val[i] = 0.0;
}              
 
double pop(void) 
{ 
   if(sp > 0) 
    return val[--sp];
   else 
   { 
     printf("pop: stack empty\n");
     return 0.0;  
   }             
}


void peek(void)
{ 
   if(sp > 0)
     printf("top element: %.2f\n", val[sp]);
   else 
     printf("peek: stack is empty\n");      
}     


int getop(char* s) 
{ 
   int next;
   int c, i; 
   
   while( (s[0] = c = getch()) == ' ' || c == '\t')
   ; 
   s[1] = '\0';    
    
   if(!isdigit(c) && c != PERIOD && c != '-') 
      return c;
   
   if(c == '-')   
   { 
     next = getch();  
     if(!isdigit(next) && next != PERIOD)
      return c; 
   
     c = next;
   }
   else { 
     c = getch();  
   }             
   
   i= 0;
   while(isdigit(s[++i] = c)) /* collect integer part */
     c = getch();
   if(c == PERIOD) /* collect fraction part */
    while(isdigit(s[++i] = c = getch())) 
       ; 
                
   s[i] = '\0';
   if(c != EOF) 
    ungetch(c);      
   
   return NUMBER;  
}


int getch(void) 
{ 
   return (bufp > 0) ? buf[--bufp] : getchar();    
}      


void ungetch(int c) 
{ 
   if(bufp < MAXBUF) 
    buf[bufp++] = c; 
   else 
    printf("ungetch: too many characters."); 
}

I can't see where you have tried to implement any argv/argc

Have you read this tutorial? Command Line Arguments in C - Cprogramming.com

Here's a snippet from my solution with no buffering.

Code:

int get_type( char * );


int main( int argc , char * argv[] )
{
    if( argc < 4 )    /* it takes at least two operands & an operator */
    {
        const char * PROGRAM_NAME = argv[ 0 ];
        printf( "Usage:\t%s [ expression ]  ( multiplication operator ( * ) must be preceded by backslash '\\' )\n" , PROGRAM_NAME );
        printf( "Example:\t%s 2 2 5 \\* +\n( 5 * 2 ) + 2\n12\n" , PROGRAM_NAME );
        return 1;
    }


    char * operand;
    int type;
    double op2;
    double value_stack[ VALUE_MAX ];


    while( ( operand = ( *++argv) ) != NULL )
    {
         //heres all the operations and whatnot
        }
}

Note that while not talking about this particular program, they do mention how to walk through the arguments starting at the bottom of page 117 and finishing with another paragraph at the top of 118. It really helped me to understand how to walk through command line arguments using pointer arithmetic.

EDIT: Ironically, I just noticed that the paragraph just mentioned leads into turning the RPN calc into a command line version called expr, which is where I pulled my source from.

Also in this example, the var operand ends up being a pointer to the beginning of the char array's, or strings, containing the arguments.