calculator! need help!! thanks!!

[vanlinkenstein]

I need to make a calculator program where the user inputs a mathematical term ( 1-2+3*4/5)
then when the user presses enter the result will be displayed.

for example:
Enter numbers to be calculated: 3+4*3
Result: 15

Here is my program. It works but only for 1 term (3*4) or (923 / 37). When i enter multiple operators (23*34+545-45) it only shows the result of the last term of the input (in this case it prints out 500). Im having a hard time doing the program specially with the precedence of the operators. Can someone help me pls? Thanks..

import java.io.*;
public class Calcu
{
public static void main(String[]args) throws IOException
{
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
String input = "";
int num1, num2, ctr = 0, sum, diff, prod, quo, result = 0;

System.out.print("Enter numbers to calculate: ");
input = br.readLine();
String arr[] = new String[input.length()];

for(int i = 0; i < input.length(); i++)
{
char c = input.charAt(i);
String s = Character.toString(c);
arr[i] = s;

if(s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/"))
ctr++;
}
int size = ctr + (ctr+1), j = 0;
String arr1[] = new String[size];

for(int i = 0; i < size; i ++)
{
arr1[i] = "";
}

for(int i = 0; i != arr.length; i++) {

if(arr[i].equals("+") || arr[i].equals("-") || arr[i].equals("*") || arr[i].equals("/"))
{
j++;
arr1[j] = arr1[j].concat(arr[i]);
j++;
}
else
{
arr1[j] = arr1[j].concat(arr[i]);
}
}
for(int i = 0; i < size; i++)
{

if(arr1[i].equals("*"))
{
num1 = Integer.parseInt(arr1[i-1]);
num2 = Integer.parseInt(arr1[i+1]);
prod = num1 * num2;
result = prod;
arr1[i-1] = Integer.toString(result);
}
if(arr1[i].equals("/"))
{
num1 = Integer.parseInt(arr1[i-1]);
num2 = Integer.parseInt(arr1[i+1]);
quo = num1 / num2;
result = quo;
arr1[i-1] = Integer.toString(result);
}
if(arr1[i].equals("+"))
{
num1 = Integer.parseInt(arr1[i-1]);
num2 = Integer.parseInt(arr1[i+1]);
sum = num1 + num2;
result = sum;
arr1[i-1] = Integer.toString(result);
}
if(arr1[i].equals("-"))
{
num1 = Integer.parseInt(arr1[i-1]);
num2 = Integer.parseInt(arr1[i+1]);
diff = num1 - num2;
result = diff;
arr1[i-1] = Integer.toString(result);
}
}
System.out.print(result);
}
}

[keang]

Use code tags when posting code and add comments to your code so we understand what you are trying to do.

[vanlinkenstein]

import java.io.*;
public class Calcu
{
    public static void main(String[]args) throws IOException
    {
        //variables
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String input = "";
        int num1, num2, ctr = 0, sum, diff, prod, quo, result = 0;

        //getting user input
        System.out.print("Enter numbers to be calculated: ");
        input = br.readLine();

        //declaring 1st array for user input
        String arr[] = new String[input.length()];

        //switching string to char to string and store it in the array
        for(int i = 0; i < input.length(); i++)
        {
            char c = input.charAt(i);
            String s = Character.toString(c);
            arr[i] = s;

            //counter for the size of next array
            if(s.equals("+") || s.equals("-") || s.equals("*") || s.equals("/"))
                ctr++;
        }
        //size of arr1 and declaration
        int size = ctr + (ctr+1), j = 0;
        String arr1[] = new String[size];

        //loop for arr1 element that assigns an empty string
        for(int i = 0; i < size; i ++)
        {
            arr1[i] = "";
        }

        //sorting operands and operators and string them to arr1
        for(int i = 0; i != arr.length; i++) 
            {            
            if(arr[i].equals("+") || arr[i].equals("-") || arr[i].equals("*") || arr[i].equals("/"))
            {
               j++;
               arr1[j] = arr1[j].concat(arr[i]);
               j++;
            } 
            else
            {
                arr1[j] = arr1[j].concat(arr[i]);
            }
        }

        //performing the operators
        for(int i = 0; i < size; i++)
        {

            if(arr1[i].equals("*"))
            {
                num1 = Integer.parseInt(arr1[i-1]);
                num2 = Integer.parseInt(arr1[i+1]);
                prod = num1 * num2;
                result = prod;
                arr1[i-1] = Integer.toString(result);
            }
            if(arr1[i].equals("/"))
            {
                num1 = Integer.parseInt(arr1[i-1]);
                num2 = Integer.parseInt(arr1[i+1]);
                quo = num1 / num2;
                result = quo;
                arr1[i-1] = Integer.toString(result);
            }
            if(arr1[i].equals("+"))
            {
                num1 = Integer.parseInt(arr1[i-1]);
                num2 = Integer.parseInt(arr1[i+1]);
                sum = num1 + num2;
                result = sum;
                arr1[i-1] = Integer.toString(result);
            }
            if(arr1[i].equals("-"))
            {
                num1 = Integer.parseInt(arr1[i-1]);
                num2 = Integer.parseInt(arr1[i+1]);
                diff = num1 - num2;
                result = diff;
                arr1[i-1] = Integer.toString(result);
            }
        }
        //prints out result
        System.out.print(result);
    }
}

sorry it is my first time posting here...hope this is ok

[keang]

My that's a complex way of attempting to solve the problem and it won't handle operator precedence.

I suggest you google for something like "evaluating math expressions" and read a few articles on the standard approaches to solving this type of problem.