Reverse Polish Notation

I am trying to write a calculator that calculates most mathematical operations in Reverse Polish Notation. However, i know im doing it right but when i try compiling it with just cc advcalc.c it gives me these errors... advcalc.c: In function ‘main’:

Code:

advcalc.c:31: error: invalid use of void expression
advcalc.c:33: error: invalid use of void expression
advcalc.c:35: error: invalid use of void expression
advcalc.c:37: error: invalid use of void expression
advcalc.c:38: warning: comparison between pointer and integer
advcalc.c:39: error: invalid use of void expression
advcalc.c:40: warning: comparison between pointer and integer
advcalc.c:41: error: invalid use of void expression
advcalc.c:42: warning: comparison between pointer and integer
advcalc.c:43: error: invalid use of void expression
advcalc.c:44: warning: comparison between pointer and integer
advcalc.c:45: error: invalid use of void expression
advcalc.c:46: warning: comparison between pointer and integer
advcalc.c:47: error: invalid use of void expression
advcalc.c:48: warning: comparison between pointer and integer
advcalc.c:49: error: invalid use of void expression
advcalc.c:50: warning: comparison between pointer and integer
advcalc.c:51: error: invalid use of void expression
advcalc.c:52: warning: comparison between pointer and integer
advcalc.c:53: error: invalid use of void expression
advcalc.c:57: error: expected declaration or statement at end of input

any input?

Code:

//RPN postfix calculator
#include <math.h>
#include <stdlib.h>
#include <stdio.h>
//53* 4 7 8 9 * + cos * +   (5*3+4*cos(7+8*9)-original numerator
//9 3 * 2 sqrt (9*3-sqrt(2))
double stack[1000];
int tos= -1;

void push(double v){
  if (tos>999){printf ("Stack Overflow\n");exit(0);}
 tos++;
  stack[++tos]=v;
}
double pop(){
  double v;
  if(tos < 0){printf("stack underflow\n");exit(0);}
  v=stack[tos--];
  //v=stack[tos--];

  return v;

}
int main(int argc,char **argv){
  int x,y,z;
  char q;
  q=argv[1][0];
  if ((q=='-')|| (('0'<=q)&&(q<='9'))){
    tos = getchar();          
            if (tos == '+')
                {printf("The sum is: %f\n",push(pop() + pop()));   } 
            if (tos == '-')
                {printf("the result is: %f\n", push(pop() - pop())); }
            if (tos == 'x')
	      {   printf("the result is: %f\n", push(pop() * pop()));}  
            if (tos == '/')
                {  printf("the result is: %f\n", push(pop() / pop()));}   
	    if (tos == "sqrt")
                {printf("the result is: %f\n", push(sqrt((double)pop())));}
	    if (tos == "qbrt")
                { printf("the result is: %f\n", push(qbrt((double)pop())));}
            if (tos == "sin")
                {  printf("the result is: %f\n", push(sin((double)pop())));    }
            if (tos == "cos")
                {  printf("the result is: %f\n", push(cos((double)pop())));   }
            if (tos == "tan")
                {printf("the result is: %f\n", push(tan((double)pop())));}
	    if (tos == "asin")
                {  printf("the result is: %f\n", push(asin((double)pop())));}
            if (tos == "acos")
                {  printf("the result is: %f\n", push(acos((double)pop())));   }
            if (tos == "atan")
                {printf("the result is: %f\n", push(atan((double)pop())));}
  }
  else{ printf("Please enter a valid integer first\n");
    exit(0);
  }

I didn't really pick through your code but you are obviously getting confused. Look at a line like this:

Code:

printf("The sum is: %f\n",push(pop() + pop()));

The return value of push, is void!, meaning absolutely nothing. So you are trying to format nothing, which obviously throws an error. I bet if you fix this problem it will solve some other problems as well.

How would i fix it? just make it pop before computing the output?

supposedly i think this one works but i cannot get it to compile. It's somebody else's in the class which i am trying to compare to..

Code:

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <ctype.h>
#include <stdlib.h>
#define  STACKSIZE  6

int  stack_pointer = 0;
int  STACKDISPLAY = 0;
double stack[STACKSIZE] = {0.0};

void
    show_stack(char message[])
{
  /*
   * this printout may be helpful for debugging and understanding what is
   * going on
   */
  int  i;
  if (!STACKDISPLAY)
    {
     return;                 /* return unless STACKDISPLAY is turned on */
    }

  printf("Displaying stack at end of function %s\nStack contents:\n\r", message);
        for (i = stack_pointer; i >= 0; i--)
            printf("stack[%d] = %f\n\r", i, stack[i]);
        printf("\n\n");
}

double
    pop_off_stack(void)
{
  double return_value;
  return_value = stack[stack_pointer]; /* return value on the top of the
                                        * stack */

  if (stack_pointer > 0) /* move the stack pointer down if not at the*/
                           /* lowest point */
        {
            stack_pointer--;
        }

  show_stack("pop_off_stack");

  return return_value;
}

double
    top_of_stack_value(void)
{
  return stack[stack_pointer]; /* just return the value on the top of the
                                * stack */
}

double
    push_onto_stack(double value)
{
  int  i;
  stack[++stack_pointer] = value; /* put value on the top of the stack */


  /*
   * check to see if stack full, if so, move down, causing the bottom value
   * to disappear
   */
  assert(stack_pointer < (STACKSIZE + 1));
  if (stack_pointer == STACKSIZE)
  {
     for (i = 0; i < STACKSIZE; i++)
        stack[i] = stack[i + 1];
     stack_pointer = STACKSIZE - 2; /* maximume of STACKSIZE-2 items max
                                           * on stack */
  }

  show_stack("push_onto_stack");
  return value;
}


int
    main(int argc, char **argv)
{
  char c, instr[80];
  double aDouble;

  while (1)
        {                         /* iterate until input file runs out or user
                                    * types q or Q */
            c = getchar();
            if (c == EOF)
                {
                    break;
                }                         /* end of file was reached, quit processing
                                            * input */

            if   (isdigit(c))         /* lame way to read a number in  gets one
                                * digit only */
                {
                    int res = c - '0';
                }

            if ((c == 'q') || (c == 'Q'))
                {
                    printf("Quiting.  Bye.\n");
                    break;                 /* quit on a Q or q */
                }

            if (c == '+')
                {
                    printf("The sum is: %f\n",
                    push_onto_stack(pop_off_stack() + pop_off_stack()));
                }
     /*
      * the above statement sums the top two elements on the stack and push the result back onto
      * the stack
      */

            if (c == '-')
                {
                    printf("the result is: %f\n", push_onto_stack(pop_off_stack() - pop_off_stack()));
                }
          /*
      * the above statement subtracts the top two elements on the stack and push the result back onto
      * the stack
      */

            if (c == '*')
                {
                    printf("the result is: %f\n", push_onto_stack(pop_off_stack() * pop_off_stack()));
                }
     /*
      * the above statement multiplies the top two elements on the stack and push the result back onto
      * the stack
      */

            if (c == '/')
                {
                    printf("the result is: %f\n", push_onto_stack(pop_off_stack() / pop_off_stack()));
                }
          /*
      * the above statement multiplies the top two elements on the stack and push the result back onto
      * the stack
      */

            if (c == "chs")
                {
		  if (
                        {
                                push_onto_stack((double)pop_off_stack()*(-1.000000))= -((double)pop_off_stack());
                                printf("the result is: %f\n", push_onto_stack((double)pop_off_stack()));
                        }
                    else if
                        {
                                push_onto_stack((double)pop_off_stack()*(-1.000000))= ((double)pop_off_stack());
                                printf("the result is: %f\n", push_onto_stack((double)pop_off_stack()*(-1.000000)));
                        }
			}


            if (c == "abs")
                {
                    printf("the result is: %f\n", push_onto_stack(abs((double)pop_off_stack())));
                }

            if (c == "sqrt")
                {
                    printf("the result is: %f\n", push_onto_stack(sqrt((double)pop_off_stack())));
                }

            if (c == "sin")
                {
                    printf("the result is: %f\n", push_onto_stack(sin((double)pop_off_stack())));
                }

            if (c == "cos")
                {
                    printf("the result is: %f\n", push_onto_stack(cos((double)pop_off_stack())));
                }

            if (c == "tan")
                {
                    printf("the result is: %f\n", push_onto_stack(tan((double)pop_off_stack())));
                }


}  /* end infinite while */

  return 0;                 /* normal termination */
}

Just look at what you are doing. You are trying to printf a (void).

I know about reverse polish notation but I don't feel like rewriting your program. I trust you know how to implement it. I am only telling you that the argument you are sending to printf is illegal. See what I mean?

Edit: Ok. I was typing while you posted that. But just look at both of their pop and push, they both return double. Hint hint.

Originally Posted by Lucid15

How would i fix it? just make it pop before computing the output?

I would suggest making another function, like top() or so, that returns the top number but doesn't remove it from the stack.

Also, is there a reason you are trying to do everything possible inside a print statement? Manipulate the stack, then print something. (If you did it that way, you might not need a top() since you would potentially still be holding onto the number you just pushed back on....)

Originally Posted by tabstop

I would suggest making another function, like top() or so, that returns the top number but doesn't remove it from the stack.

Also, is there a reason you are trying to do everything possible inside a print statement? Manipulate the stack, then print something. (If you did it that way, you might not need a top() since you would potentially still be holding onto the number you just pushed back on....)

Im actually pretty confused as someone helped me. Can you do an example of this on the + function?

ok so i got someone to show me their program which i now understand. but i need to know how i can implement the other functions such as sin cos and all of that ...

Code:

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

double stack[1000];
int tos;

void push(double v){
  if(tos>998){
    printf("Stack overflow.\n"); exit(0);}
  tos++;
  stack[tos]=v;
}

double pop(){
  double v;
  if(tos<0){
    printf("Stack underflow.\n"); exit(0);}
  v=stack[tos];
  tos--;
  return v;
}

int main(int argc, char **argv)
{
  double x,y,z,sum;
  int k,j,i,c; 
  tos=-1;
  j=1;
  i=argc-1;

  //work on while loop

while(0<i){
  k=0;
  c=1;
  if(argv[j][k]=='+'){
    y=pop();
    x=pop();
    z=x+y;
    push(z);}
   
  else if(argv[j][k]=='-'){
    y=pop();
    x=pop();
    z=x-y;
    push(z);}
  else if(argv[j][k]=='x'){
    y=pop();
    x=pop();
    z=x*y;
    push(z);}
  else if(argv[j][k]=='/'){
    y=pop();
    x=pop();
    z=x/y;
    push(z);}

  // else if((argv[j][k]=='c') && (argv[j][k+3]==0)){
     //  x=pop();
    //  z=cos(x);
   // push(z);}

  // else if((argv[j][k]=='s') && (argv[j][k+1]=='i')){
  //  x=pop();
  //  z=sin(x);
  //  push(z);}

  // else if((argv[j][k]=='s') && (argv[j][k+1]=='q')){
  //  x=pop();
  //  z=sqrt(x);
  //  push(z);}

  //CAREFUL WITH THIS ONE
  else if((argv[j][k]=='e') && (argv[j][k+1]=='x')){
      x=pop();
      z=1;
      while(x>0){
	z=z*2.7182818284590452353602874;
	x--;}
    }



  else{
      while(argv[j][k]!=0){
	k++;}
      k=k-1;
      sum=0;
      while(k>=0){
	sum=sum+((argv[j][k]-48)*c);
	c=c*10;
	k--;
      }
   	push(sum);
    }
    j++;
    i--;
 }
 printf("= %lf\n", z);

}