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equation evaluator

tester12 (2)
hello everyone,

I have written a code 2 calculate an equation entered by user. I have to prioritize the operators in order of precedence with ( coming first then * and / then + and - . I am having a logical error in my code, but I don't know how to solve it. The problem is with

sub_equation.replace(sub_equation.at(position[i]-1),2,y);

and

equation.replace(equation.at(position[i]-1),2,y);

The error says that there is no enough memory allocation
Your help is needed. Thanks :)


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#include <iostream>
#include <iomanip>
#include <fstream>
#include <sstream>
#include <string>
#include <iomanip>
#include <stack>
using namespace std;

void main ()
{
	string equation, sub_equation="",y="";
	stringstream ss;
	int brace_r, brace_l;
	//stack <char> s;
	cout<<"Please enter your equation"<<endl;
	getline(cin,equation);
	/*
	string x="abcd";
	equation.replace(3,7,x);
	cout<<equation<<endl;
	*/
	int l=equation.length();
	const char *eq; 
	eq= equation.c_str(); //converting sub_equation to char array

	int i,j,k, counter, operators,x;
	int position[50];
	brace_r=equation.find('(');
	brace_l=equation.find(')');
	do
	{


		while (brace_r>0 && brace_r<50) //find all braces in equation
		{
			if (brace_l>0 && brace_l<50) //making sure that braces match
			{
				sub_equation=equation.substr(brace_r,brace_l-brace_r+1); //copying chars between braces in new string
				//sub_equation1=sub_equation; 
				const char *sub_eq; 
				sub_eq= sub_equation.c_str(); //converting sub_equation to char array
				counter=0; //counter for operators between braces
				operators=0; //counter for 
				
				for (k=0;k<50;k++) //array to determine location of operators
					position[k]=-1;
				j=0;
				for (i=0; i<sub_equation.length();i++)
				{
					if (sub_eq[i]==('*') || sub_eq[i]==('/'))
					{
						counter++;
						position[j]=i;
						j++;
					}
				}

				for (i=0; i<sub_equation.length();i++)//loop to evaluate & replace value of data in braces
				{
					if (counter!=0)
					{

						if (position [i]!=-1)
						{
							if (sub_equation.at(position[i])=='*')
							{
								x=int(sub_equation.at(position[i]-1))*int(sub_equation.at(position[i]+1));
								ss<<x;
								ss>>y;
								counter--;
							    sub_equation.replace(sub_equation.at(position[i]-1),2,y);
							//	sub_equation.erase(sub_equation.at(position[i]-1),2);
							//	sub_equation.insert(sub_equation.at(position[i]-1),y);

							}

							else if (sub_equation.at(position[i])=='/')
							{
								x=int(sub_equation.at(position[i]-1))/int(sub_equation.at(position[i]+1));
								counter--;
								ss<<x;
								ss>>y;
								sub_equation.replace(sub_equation.at(position[i]-1),2,y);
							//	sub_equation.erase(sub_equation.at(position[i]-1),2);
							//	sub_equation.insert(sub_equation.at(position[i]-1),y);

							}
						}
						
					}
					else 
						break;
					
				}

				counter=0;
				for (k=0;k<50;k++)
					position[k]=-1;
				for (i=0; i<sub_equation.length();i++)
				{
					j=0;

					if (sub_eq[i]==('+') || sub_eq[i]==('-'))
					{
						counter++;
						position[j]=i;
						j++;
					}
				}


				for (i=0; i<sub_equation.length();i++)//loop to evaluate&replace value of data in braces
				{
					if (counter!=0)
					{

						if (position [i]!=-1)
						{
							if (sub_equation.at(position[i])=='+')
							{
								x=int(sub_equation.at(position[i]-1))+int(sub_equation.at(position[i]+1));
								counter--;
								ss<<x;
								ss>>y;
								sub_equation.replace(sub_equation.at(position[i]-1),2,y);
								//sub_equation.erase(sub_equation.at(position[i]-1),2);
								//sub_equation.insert(sub_equation.at(position[i]-1),y);
							}

							else if (sub_equation.at(position[i])=='-')
							{
								x=int(sub_equation.at(position[i]-1))-int(sub_equation.at(position[i]+1));
								counter--;
								ss<<x;
								ss>>y;
								
								sub_equation.replace(sub_equation.at(position[i]-1),2,y);
								//sub_equation.erase(sub_equation.at(position[i]-1),2);
								//sub_equation.insert(sub_equation.at(position[i]-1),y);

							}
							else break;


						}
					}
					else 
						break;
				}

			}
		}
		ss<<sub_equation;
		ss>>y;
		equation.replace(brace_r, brace_l-brace_r+1, y);
		counter=0; //counter for operators between braces
		operators=0; //counter for 
		for (k=0;k<50;k++)
			position[k]=-1;
		for (i=0; i<equation.length();i++)
		{
			j=0;
			if (eq[i]==('*') || eq[i]==('/'))
			{
				counter++;
				position[j]=i;
				j++;
			}
		}
		for (i=0; i<equation.length();i++)//loop to evaluate & replace value of data in braces
		{
			if (counter!=0)
			{
				if (position [i]!=-1)
				{
					if (equation.at(position[i])=='*')
					{
						x=int(equation.at(position[i]-1))*int(equation.at(position[i]+1));
						ss<<x;
						ss>>y;
						counter--;
						equation.replace(equation.at(position[i]-1),2,y);
						//		equation.erase(equation.at(position[i]-1),2);
						//		equation.insert(equation.at(position[i]-1),y);

					}
					else if (equation.at(position[i])=='/')
					{
						x=int(equation.at(position[i]-1))/int(equation.at(position[i]+1));
						counter--;
						ss<<x;
						ss>>y;
						equation.replace(equation.at(position[i]-1),2,y);
						//		equation.erase(equation.at(position[i]-1),2);
						//		equation.insert(equation.at(position[i]-1),y);

					}
				}
			}
		}
	}while (equation.find('+')<50 && equation.find('-')<50 && equation.find('*')<50 && equation.find('/')<50);
		cout<<"The inserted equation equals "<<equation<<endl;

		system ("pause");
}
Last edited on
TinyTeeTree (73)
once again, if you want to paste code in the forum use the "Source code" button tagged with <> in the Format: button box. Anything you put between the {code} and {/code} willhave all its indentation intact, otherwise we aint gonna even try reading this.
Last edited on
tester12 (2)
ok sorry. i am just new to the forum and i didnt know how 2 do it. thanx 4 ur feedback :)
TinyTeeTree (73)
another pro tip of the day,

***use functions...!!!***

I mean, whats the point of equation evaluator if its not in a function. If you make the same code just function oriented, then you can use that function in other code as well. lets say tomorow you want to make some algorythm thingy majingy, which could use lets say an equation evaluator. then all you'll have to do is #include the function defenition/implementation and you can use it.
TinyTeeTree (73)
anyway, i used the debbuger a little bit, and your code is fuuuuulll of bugs, its not just a little bit but let me get you started.

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for (i=0; i<sub_equation.length();i++)
{
	j=0;

	if (sub_eq[i]==('+') || sub_eq[i]==('-'))
	{
		counter++;
		position[j]=i;
		j++;
	}
}


j, whatever it does or supposed to do, is always 0 no matter what, the way you reset it right after you increment it assures you that it will stay 0.

what you probably meant was this
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j=0;
for (i=0; i<sub_equation.length();i++)
{

	if (sub_eq[i]==('+') || sub_eq[i]==('-'))
	{
		counter++;
		position[j]=i;
	}
	j++;
}


further more your sub_equation does not reduce brackets () meaning that for equation = 3+(4+4)
sub_equation = (4+4)

are you taking that into consideration?

further more 
 
 
x=int(sub_equation.at(position[i]-1))+int(sub_equation.at(position[i]+1));


this line of code doesnt work properly, I know its a drag to convert chars to digits but basically you need to look into the ascii table to know what each char stands for basically '4' = 52 so your x will evaluate to 52+52 if the sub_equation is (4+4). the solution is to subtract 48 from the char representation to get the digit correctly.

http://images.search.conduit.com/ImagePreview/?q=ascii&ctid=CT2296690&SearchSource=4&FollowOn=true&PageSource=Results&SSPV=&CUI=&UP=&UM=&start=0&pos=1

this picture should shed some light.


you probably have more bugs,


I highly recommend that you learn to program step by step, writing and testing small portions of code at a time so you can fix these small errors as they appear, and the do appear, right in the rear.
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