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Adding numbers using button to a textbox

I'm new to programming and I have a problem. I have two buttons and a textbox. When I press the button, a number will show on the textbox, but when I press the second button the number in the textbox overwrites it and replaces it instead of adding to it in the textbox. How do I fix this? I want the values to add instead of replacing it.
public partial class Form1 : Form
{
int value1 = 0;
int value2 = 0;
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
value1++;
textBox1.Text = value1.ToString();
}
private void button2_Click(object sender, EventArgs e)
{
value2 += 2;
textBox1.Text = value2.ToString();
}
}
}

If you want to add two integers and assign the result back to textBox1 you have to
Parse textBox1.Text to integer: int.Parse(textBox1.Text)
Sum up values: int.Parse(textBox1.Text) + value2
Convert the outcome back to string: (...).ToString()
Implementation:
private void button2_Click(object sender, EventArgs e) {
value2 += 2;
textBox1.Text = (int.Parse(textBox1.Text) + value2).ToString();
}
Edit: If there's a possibility that textBox1.Text doesn't contain a valid integer value (say, textBox1.Text is empty) you can use int.TryParse:
private void button2_Click(object sender, EventArgs e) {
if (int.TryParse(textBox1.Text, out var v)) {
value2 += 2;
textBox1.Text = (v + value2).ToString();
}
else {
//TODO: textBox1.Text is not a valid integer; put relevant code here
}
}

You're using two separate variables (value1 and value2 above) to store the results of each button click, depending in which button was clicked. Think of it like this:
On program start:
value1 = 0
value2 = 0
User clicks button 1, which executes button1_Click. This increments value1 (via value1++), so the two variables look like this:
value1 = 1
value2 = 0
User then clicks button 2, which executes button2_Click. This sets value2 to whatever was previously in value2 + 2. However, note that the value of value1 is unchanged:
value1 = 1
value2 = 2
By having separate variables, each button click is operating on a different value. I would modify your code so there is only one value variable that both _Click functions modify.

Add this line:
textBox1.Text = (int.parseInt(textBox1.Text) + value2).toString();
after
value2 += 2;
into your button2_click method:

Unwanted Char Appears

I am beginner , am trying to create a calculator. the way of the code working is there is a method for summing and one for subtraction ETC.
when i call the subtraction method unwanted minus appears before the answer in the textbox ( i know my code could be using harder way to do the same purpose but i am just beginner trying to do some code )
double rat;
byte operations;
public void TheEqualMinus(double earlier) //Substraction Operation Method
{
double _minus;
_minus = Convert.ToDouble(result.Text);
double last = _minus - earlier;
result.Text = last.ToString();
}
private void button15_Click(object sender, EventArgs e)
{
//The Subtract Button
operations = 2;
rat = Convert.ToDouble(result.Text);
label1.Text = rat + " -";
result.Text = "";
}
private void button4_Click(object sender, EventArgs e)
{
// equal button
NewText = true; //boolean to newtext
switch (operations)
{
case (1): //addition
TheEqualSum(rat);
label1.Text = "";
break;
case (2): //substraction
TheEqualMinus(rat);
label1.Text = "";
break;
}
}
and the answer output becomes " - The Correct Answer i want "
ex. 9-6 = -3
so any ideas how to remove this minus ?

As per the comments above, this was fixed by simply changing this:
double last = _minus - earlier;
to this:
double last = earlier - _minus;

How can I find the last character of a textbox text?

I am a beginner in C#. I am making a web calculator like Microsoft Desktop calculator with the help of asp.net. But I'm stuck at one place. My code for Plus, minus, multiply or div is like:
protected void btnPlus_Click(object sender, EventArgs e)
{
if (txtBox1.Text.EndsWith("+"))
{
txtBox1.Text = txtBox1.Text;
}
else
{
txtBox1.Text = txtBox1.Text + "+";
ViewState["Operation"] = "+";
}
}
But I want to check this condition for all operations like minus, multiply and divide. I don't want Plus, Minus, Multiply or Div signs appear in the textbox.

You can store all your operators in a string constant and check if the last character is contained in that string:
private const string OPERATORS = "+-/*";
protected void btnPlus_Click(object sender, EventArgs e)
{
if (string.IsNullOrEmpty(txtBox1.Text) || // check if string is empty
OPERATORS.Contains(txtBox1.Text.Last())) // or if last character is a operator
{
txtBox1.Text = txtBox1.Text;
}
else
{
txtBox1.Text = txtBox1.Text + "+";
ViewState["Operation"] = "+";
}
}

You can do something like the following:
Extract last character
Based on the character assign operator to the view state
If it is any operator then remove them from the textbox
Finally do the operation
if (txtBox1.Text != "")
{
char last_char = txtBox1.Text[txtBox1.Text.Length - 1];
switch (last_char)
{
case '+':
ViewState["Operation"] = "+";
txtBox1.Text.Remove(txtBox1.Text.Length - 1);
break;
case '-':
ViewState["Operation"] = "-";
txtBox1.Text.Remove(txtBox1.Text.Length - 1);
break;
// do the same for all operators
default:
break;
}
}

Input string was not in a correct format in double.Parse

I am new to C#. I'm trying to make a calculator, but the following error occurred:
Input string was not in a correct format.
This is the summary of the code:
double num1, num2, result;
private void button14_Click(object sender, EventArgs e)
{
num1 = Convert.ToDouble(textBox1.Text);
textBox1.Text = String.Empty;
num2 = double.Parse(textBox1.Text); **//ERROR OCCURED HERE**
result = num1 - num2;
}
private void button13_Click(object sender, EventArgs e)
{
num1 = Convert.ToDouble(textBox1.Text);
textBox1.Text = String.Empty;
num2 = System.Double.Parse(textBox1.Text); **//ERROR OCCURED HERE**
result = num1 + num2;
}
How to convert string to a double type?

Also remember that the Parse method is relying on the culture of your operating system to perform the conversion, so try to change your code to
num2 = double.Parse(textBox1.Text, CultureInfo.InvariantCulture);
You might also consider to use the
double.TryParse
method for better exception handling.

What are you trying to achieve with this code? It seems that your algorythm is wrong.
Like others said, this code
textBox1.Text = String.Empty;
num2 = double.Parse(textBox1.Text);
will throw an Exception because an empty string cannot be converted to Double!
So, I'm wondering why did you reset your field. I thought about it for a while, and maybe I got what are you trying to do. Let's say you type a number in TextBox1. Then you press the "-" button to subtract and then you want to enter the second number to view the result. Is this the case? If it is, the code you wrote is not going to wait for your next input!
In fact, when you click the button, it just executes all the lines you wrote. I'd write something like this instead.
double num1, num2, result;
string operation;
private void button14_Click(object sender, EventArgs e) //Minus Button
{
if (textBox1.Text != String.Empty) //Added if statement to see if the textBox is empty
num1 = Convert.ToDouble(textBox1.Text);
else
num1 = 0; //If textBox is empty, set num1 to 0
textBox1.Text = String.Empty;
operation = "-";
}
private void button13_Click(object sender, EventArgs e) //Equals Button
{
if (textBox1.Text != String.Empty)
num2 = Convert.ToDouble(textBox1.Text);
else
num2 = 0;
if (operation == "-")
{
result = num1 - num2;
textBox1.Text = Convert.ToString(result);
}
if (operation == "+")
{
//You got it
}
//And so on...
}
EDIT: If the string is empty, this is going to always throw Exceptions, so I added a control. If the string is empty, value becomes zero.

Since you have cleared the textbox on the previous line, the Parse conversion fails.
textBox1.Text = String.Empty;
num2 = double.Parse(textBox1.Text);
How will it convert String.Empty to Double?
The way of doing it is not right.
For example, if the "+" button is clicked, you have to check whether there was already a number. If so,, add the numbers and display the result:
Double num;
private void Add_Click(object sender, EventArgs e)
{
If (num != null)
{
num == num + Convert.ToDouble(textBox1.Text);
}
else
{
num1 == Convert.ToDouble(textBox1.Text);
}
textBox1.Text = num;
}

Seems like num2 value should be fetched from textbox2 not textbox1(You are setting textbox1.text to empty and trying to parse it to double again)
//You are setting textbox1 to empty
textBox1.Text = String.Empty;
//here trying to parse it to double
num2 = double.Parse(textBox1.Text);
Also don't use Convert.ToDouble(textBox1.Text) directly. if users type non numeric values your code will crash. first check if its a valid number, always use doube.TryPrase()
double num1;
double.TryParse(textBox1.Text, out num1);

Your code seems hard to understand whats the use of button_13 and button_14;
I will assume your trying to do this:
bool ifNew = true;
double num1 ,num2,result;
private void Add_Click(object sender, EventArgs e))
{
if(ifNew)
{
num1 = Convert.ToDouble(textBox1.Text);
textbox1.Clear();
ifNew = false;
result += num1;
}
else
{
num2 = Convert.ToDouble(textBox1.Text);
textbox1.Clear();
result += num2;
num1 = 0D;
num2 = 0D;
ifNew = true;
}
}
private void Equals_Click(object sender, EventArgs e)
{
textboxl.Text = string.Format("{0:N}",result);
}
Or you could use Double.Parse in my Convert.ToDouble
It depends on your operation but I am visualizing
how to do add operation you can change and edit this
depends on your operation

How do I stop a single button from hiding my textbox during a specific event?

I have two questions:
1) Is this the correct way to make my default value = 0 for variables, then pass a value given by the user into that variable?
protected void btnCheck_Click(object sender, EventArgs e)
{
lblYesNo.Text = "";
//default int values are set to 0
int remainder = 0;
int guess = 0;
remainder = int.Parse(txtRemainder.Text);
guess = int.Parse(txtAnswer.Text);
answer = (int)Session["answer"];
if (guess == answer)
{
lblYesNo.Text = lblYesNo.Text + "Correct!";
}
else
{
lblYesNo.Text = lblYesNo.Text + "Try Again..";
}
}//END Check Answer
2) how can I stop the Check_Click(submit button) from hiding the txtRemainder(textbox)? The reason it 'auto-hides' now is because I set the default value to 'txtRemainder.Visible = false;' in the Page_Load, which will make it hide unless the math problem is division. When I click on the btnDiv_Click(divide button) it resets it to 'txtRemainder.Visible = true;', because this provides a division question to be solved.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class BasicMath : System.Web.UI.Page
{
int number1;
int number2;
int answer;
protected void Page_Load(object sender, EventArgs e)
{
txtRemainder.Visible = false;
}
protected void GetRandom()
{
Random rand = new Random();
number1 = rand.Next(0, 10);
number2 = rand.Next(0, 10);
txtAnswer.Text = "";
txtRemainder.Text = "";
lblYesNo.Text = "";
}//END Get Random Number
protected void btnAdd_Click(object sender, EventArgs e)
{
GetRandom();
lblEquation.Text = number1.ToString() + " + " + number2.ToString();
answer = number1 + number2;
Session["answer"] = answer;
}//END Addition Button
protected void btnSub_Click(object sender, EventArgs e)
{
GetRandom();
if (number2 > number1)
{
answer = number2 - number1;
lblEquation.Text = number2.ToString() + " - " + number1.ToString();
}
else
{
answer = number1 - number2;
lblEquation.Text = number1.ToString() + " - " + number2.ToString();
}
Session["answer"] = answer;
}//END Subtraction Button
protected void btnMult_Click(object sender, EventArgs e)
{
GetRandom();
lblEquation.Text = number1.ToString() + " x " + number2.ToString();
answer = number1 * number2;
Session["answer"] = answer;
}//END Multiplication Button
protected void btnDiv_Click(object sender, EventArgs e)
{
Random rand = new Random();
number1 = rand.Next(1, 10);
number2 = rand.Next(1, 10);
/*will only display the txtRemainder(textbox) while using the Divide button,
txtRemainder will auto-hide when using another button because
it's default setting of '.Visible = false' is placed in the Page_Load*/
txtRemainder.Visible = true;
lblEquation.Text = number1.ToString() + " / " + number2.ToString();
answer = number1 / number2;
Session["answer"] = answer;
}//END Division Button
protected void btnCheck_Click(object sender, EventArgs e)
{
lblYesNo.Text = "";
//default int values are set to 0
int remainder = 0;
int guess = 0;
remainder = int.Parse(txtRemainder.Text);
guess = int.Parse(txtAnswer.Text);
answer = (int)Session["answer"];
if (guess == answer)
{
lblYesNo.Text = lblYesNo.Text + "Correct!";
}
else
{
lblYesNo.Text = lblYesNo.Text + "Try Again..";
}
}//END Check Answer
}
If this question doesn't make sense please ask for clarification.

Question 1:
Yes, that is the correct way to initialize your variables to default values of zero, although int variables are initialized to zero by default, so even if you omitted the assignment, they would still default to zero.
The method you're using to accept the user input is correct, but could throw an exception if the values entered by the user are not Int32 values (think 3.2). As it stands, you have no try..catch blocks to deal with these exceptions. You could either add these try..catch blocks, or you could use the TryParse() method to check that the values are valid. For example:
protected void btnCheck_Click(object sender, EventArgs e)
{
lblYesNo.Text = "";
//default int values are set to 0
int remainder = 0;
int guess = 0;
if (!Int32.TryParse(txtRemainder.Text, out remainder))
{
// do something here to inform the user that remainder is invalid
return;
}
if (!Int32.TryParse(txtAnswer.Text, out remainder))
{
// do something here to inform the user that answer is invalid
return;
}
answer = (int)Session["answer"];
if (guess > answer)
{
lblYesNo.Text = lblYesNo.Text + "Try Again..";
}
else if (guess < answer)
{
lblYesNo.Text = lblYesNo.Text + "Try Again..";
}
else
{
lblYesNo.Text = lblYesNo.Text + "Correct!";
}
}//END Check Answer
TryParse() will convert the value into the output variable if it's a valid value & return true to indicate success, otherwise it will return false if it was not able to perform the conversion.
Question 2:
In order to hide txtRemainder when the page first loads & then to keep it hidden if any button was clicked other than btnDiv, here is a proposed solution. First, the code:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack) {
lblTest.Visible = false;
} else {
foreach (string ctrl in Request.Form) {
Control c = FindControl(ctrl);
if (c is Button) {
txtRemainder.Visible = c.ID == "btnDiv";
return;
}
}
}
}
Now for some explaining. When the page initially loads, the label is hidden (by the !IsPostBack check). If the request is indeed a postback, we go through the collection of returned form controls (contained in the Request.Form collection) & check to see if a button is present that could have caused the postback. Buttons are rendered in the HTML as <input type="submit" .. /> elements, and upon postback, only the button that was clicked is sent back in the Form collection, even if there are multiple submits on the page. A more detailed explanation can be found here
Now, if a button did indeed cause the postback, then we check to see if this button was btnDiv. If it was, the comparison returns true & txtRemainder is displayed. If not, it is hidden.
This way, there is no need to show or hide txtRemainder in each event handlers. You wouldn't even need to set it to visible in the event handler for btnDiv.
EDIT
Based on the requirement listed in the comments, I've altered my answer to question 2 so as to provide an alternative method to having to show or hide the label in each button event.

Question1:
If you are using .Net 4.0 and up, consider using the TryParse method, and check the result for success, this way you have better control over parsing values and trapping exceptions
e.g.
int number = 0;
bool result = false;
result = int.TryParse("123", out number);
if (!result)
{
throw new InvalidCastException("Error converting number");
}
Question2:
It looks like you're using Asp.Net, so try testing for Page.IsPostBack in your Page_Load event, this way you can determine whether the page loads because of an initial load, or because you sent data to the server i.e. clicked a button.
Hope this helps!