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:

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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

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any input?

Code:

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//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);
  }

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

Code:

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

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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:

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#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 */
}

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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.

Quote:

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Originally Posted by Lucid15

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

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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....)

Quote:

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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....)

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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:

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#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);

}

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