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I don't know why my output is 0 when I enter an equation

C
#include<stdio.h>
#include <stdlib.h>
#include<string.h>
#include <ctype.h>
#include "boolean.h"
#include "alg2rpn.h"
#include "cstack.h"
#include "fstack.h"
#include "rpn.h"


boolean is_op(char op);

boolean is_op(char op){
if((op=='+')||(op=='-')||(op=='*')||(op=='/'))
			return TRUE;
		else 
			return FALSE;

}


int perc(char e);

int perc(char e) {

               int pr;
		if((e=='+')||(e=='-')){
			pr=1;
			return pr;
		}
		
		else if((e=='*')||(e=='/')){
			pr=5;
			return pr;
		}
	}

char alg2rpn(char input[]){
float rpneval(char input[]){
cstack top;
int state=0;
int i=0;
int o=-0;
char c,output[101];

init_cstack(&top);

while(1){
switch(state){
case 0: 
        i++;
        c=input[i];
        if(isdigit(c))
        state=1;
        else if(is_op(c))
        state=2;
        else if(c=='(')
        state=3;
        else if(c==')')
        state=4;
        else if(c=='\0')
        state=5;
        else
        state=6;
        break;

case 1: output[o]=input[i];
        o++;
        i++;
        while(isdigit(input[i]) || input[i] =='.')
        output[o]=input[i];
        o++;
        i++;
        output[o] =' ';
        o++;
        i--;
        state=0;
        break;

case 2: 
    while ((!cis_empty(top))&&(is_op(top->data))&&(perc(c))<=(perc(top->data)));
     output[o]= cpop(&top);
     o++;
     output[o] =' ';
     o++;
     if (!cis_full()){
                      cpush(&top,(input[i]));
		      }
	              else {
                         printf("Error! stack is full\n");
	                 exit (0);
                      }
                      state=0;
                      break;
     

case 3: 
         if (!cis_full()){
                      cpush(&top,(input[i]));
		      }
	              else {
                         printf("Error! stack is full\n");
	                 exit (0);
                      }
                      state=0;
                      break;

case 4: 
        while((!cis_empty(top))&&(i!='(')){
        output[o]=cpop(&top);
        o++;
        output[o] = ' ';
        o++;
        }
        if(!cis_empty(top))
        cpop(&top);
        else {
             printf("Error! mismatched parenthesis\n");
	 exit (0);
        }
        state=0;
        break;

case 5: 
        while((!cis_empty(top))&&(is_op(top->data))) {
        output[o]=cpop(&top);
        o++;
        output[o] =' ';
        o++;
        if(!cis_empty(top)){
        printf("Error! leftovers parenthesis\n");
	exit (0);
        }
        output[o] ='\0';
        printf("output in RPN format: %s\n", output);
        return rpneval(output);
        break;

case 6:
       printf("Error!! Wrong input\n");
       exit (0);
       break;

       }
    }
     }
}
}


What I have tried:

I have searched places, and i'm a bit confused on what to do
Posted
Updated 30-Apr-22 20:04pm
v2
Comments
Patrice T 30-Apr-22 20:38pm    
Show code that we can run.
Show sample input that exhibit the problem.

1 solution

That code won't even compile as C has no concept of "local functions":
C
char alg2rpn(char input[]){
float rpneval(char input[]){
cstack top;
And I'm not going to try and work out what it might do if it did compile as it's too badly indented, undocumented, and full of single or two character variables which I have no idea what they are for.

Even if it did compile, I have no way to run it as you don't have a main function to start the app running so I have no idea what you are actually calling ...

To be honest, that code looks like it was thrown together without much thought before diving into code, and that's always a bad idea.

Me? I'd throw it all away, and start again - thinking and planning for a good time first before I opened an editor! I'd indent it correctly, so it can be easily written, and use variable names that describe what they are there for instead of being easy to type. And I'd test it while I was writing it as well, so I knew that a bit of code worked before I wrote some more.

But that's up to you. If you do have code that compiles, code that runs, then you can debug it. Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
C
int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

But I'd chuck it as start again. This may help: How to Write Code to Solve a Problem, A Beginner's Guide[^]
 
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Comments
CPallini 1-May-22 13:07pm    
5.

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