问题
I am designing a basic calculator using C#. I am facing difficulties while I am entering a decimal point. Example, if I am entering .8 then it gives me 0.8 which is correct if there is nothing on the display screen but after that if I am entering the decimal symbol, then also it accepts it that is 0.8..... I want only one decimal symbol to be accepted for one number. My code is
private void btn_Decimal_Click(object sender, EventArgs e)
{
if (txt_Result.Text == "" || LastcharIssymbol==true)
{
txt_Result.Text = txt_Result.Text + 0 + ".";
}
else
txt_Result.Text = txt_Result.Text + ".";
}
Here, if I am entering 0.9.999 then also it accepts and if I am entering 999..... then also it accepts. I want only one decimal symbol to be accepted for one number that is 999.999. Please help me. Also I am adding two additional labels that can show the current system date and time. I am unable to show the date as well as the time but I am able to show the date and time using VB.Net. I don't know where I am getting the errors. My whole code is
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace CS_Calculator
{
public partial class Form1 : Form
{
Boolean LastcharIssymbol {get;set;}
string op;
double a, memory;
public Form1()
{
InitializeComponent();
}
private void btn_1_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "1";
LastcharIssymbol= false;
}
private void btn_2_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "2";
LastcharIssymbol = false;
}
private void btn_3_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "3";
LastcharIssymbol = false;
}
private void btn_4_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "4";
LastcharIssymbol = false;
}
private void btn_5_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "5";
LastcharIssymbol = false;
}
private void btn_6_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "6";
LastcharIssymbol = false;
}
private void btn_7_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "7";
LastcharIssymbol = false;
}
private void btn_8_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "8";
LastcharIssymbol = false;
}
private void btn_9_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "9";
LastcharIssymbol = false;
}
private void btn_0_Click(object sender, EventArgs e)
{
txt_Result.Text = txt_Result.Text + "0";
LastcharIssymbol = false;
}
private void btn_Decimal_Click(object sender, EventArgs e)
{
if (txt_Result.Text == "" || LastcharIssymbol==true)
{
txt_Result.Text = txt_Result.Text + 0 + ".";
}
else
txt_Result.Text = txt_Result.Text + ".";
}
private void btn_Plus_Click(object sender, EventArgs e)
{
if(txt_Result.Text=="" || LastcharIssymbol)
{
MessageBox.Show("Please Enter first number to perform the addition operation.");
}
else
{
op = "+";
txt_Result.Text = txt_Result.Text + op;
LastcharIssymbol=true;
}
}
private void btn_Minus_Click(object sender, EventArgs e)
{
if (txt_Result.Text == "" || LastcharIssymbol)
{
MessageBox.Show("Please enter first number to erform the substraction operation.");
}
else
{
op = "-";
txt_Result.Text = txt_Result.Text + op;
LastcharIssymbol = true;
}
}
private void btn_Division_Click(object sender, EventArgs e)
{
if (txt_Result.Text == "" || LastcharIssymbol)
{
MessageBox.Show("Please enter first number to perform the division operation.");
}
else
{
op = "/";
txt_Result.Text = txt_Result.Text + op;
LastcharIssymbol = true;
}
}
private void btn_Mult_Click(object sender, EventArgs e)
{
if (txt_Result.Text == "" || LastcharIssymbol)
{
MessageBox.Show("Please enter first number to perform the multiplication operation.");
}
else
{
op = "*";
txt_Result.Text = txt_Result.Text + op;
LastcharIssymbol = true;
}
}
private void btn_Equal_Click(object sender, EventArgs e)
{
}
private void button4_Click(object sender, EventArgs e)
{
txt_Result.Text = "";
}
private void btn_Clear_All_Click(object sender, EventArgs e)
{
txt_Result.Text = "";
op = "";
a = 0;
memory = 0;
}
private void btn_Memory_Click(object sender, EventArgs e)
{
memory = Convert.ToDouble(txt_Result.Text);
}
private void btn_Show_Memory_Click(object sender, EventArgs e)
{
txt_Result.Text = memory.ToString();
}
}
}
回答1:
if (!txt_Result.Text.Contains("."))
if(txt_Result.Text == string.Empty)
txt_Result.Text = "0.";
else
txt_Result.Text += ".";
else
MessageBox.Show("more dots are not allowd");
for the case you have text like '11.9+12' which has operations in it you can do the following
string formula = "11.9/1.2*99.9+19";
string lastPiece = formula.Split(new char[] { '+', '-', '*', '/' })[formula.Split(new char[] { '+', '-', '*', '/' }).Count() - 1];
if (!lastPiece.Contains('.')) formula += ".";
//adds dot
lastPiece = formula.Split(new char[] { '+', '-', '*', '/' })[formula.Split(new char[] { '+', '-', '*', '/' }).Count() - 1];
if (!lastPiece.Contains('.')) formula += ".";
//does not add dot
MessageBox.Show(formula);
//output : 11.9/1.2*99.9+19.
回答2:
You should disable the decimal once it is clicked and enable it again if any of the operator or 'C' is pressed.
回答3:
You could use decimal.TryParse to test whether the string is a valid decimal number. If not, such as if your input has two decimal points, then the TryParse call fails.
TryParse is a good option because there can be many issues with an entered number besides a doubled decimal point such as... a triple decimal point, a misplaced minus sign, alpha chars etc.
Try:
private void btn_Decimal_Click(object sender, EventArgs e)
{
decimal num;
if (!Decimal.TryParse(txt_Result.Text, out num))
{
MessageBox.Show(txt_Result.Text + " is not a valid number.");
return;
}
if (txt_Result.Text == "" || LastcharIssymbol==true)
txt_Result.Text = txt_Result.Text + 0 + ".";
else
txt_Result.Text = txt_Result.Text + ".";
}
回答4:
private void txtPrice_KeyPress(object sender, KeyPressEventArgs e)//textprice key pressed
{
if ((e.KeyChar < '0' || e.KeyChar > '9') && (e.KeyChar != '\b') && (e.KeyChar != '.'))
{
e.Handled = true;
}
else
{
e.Handled = false;
}
if (Char.IsControl(e.KeyChar))
{
e.Handled = false;
}
else if (Char.IsNumber(e.KeyChar) || e.KeyChar == '.')
{
TextBox tb = sender as TextBox;
int cursorPosLeft = tb.SelectionStart;
int cursorPosRight = tb.SelectionStart + tb.SelectionLength;
string result = tb.Text.Substring(0, cursorPosLeft) + e.KeyChar + tb.Text.Substring(cursorPosRight);
string[] parts = result.Split('.');
if (parts.Length > 1)
{
if (parts[1].Length > 2 || parts.Length > 2)
{
e.Handled = true;
}
}
}
回答5:
Change your last else to:
else if (!txt_Result.Text.Contains (".")) {
txt_Result.Text = txt_Result.Text + ".";
}
Or consider disabling the decimal point button.
You should probably do some validation on the value to ensure it is a valid number.
回答6:
**Another example , 100% **
private void txtPrice_KeyPress(object sender, KeyPressEventArgs e)
{
if (txtPrice.Text.Length == 0)
{
if (e.KeyChar == '.')
{
e.Handled = true;
}
}
if (!char.IsDigit(e.KeyChar) && e.KeyChar != 8 && e.KeyChar != 46)
{
e.Handled = true;
}
if (e.KeyChar == '.' && txtPrice.Text.IndexOf('.') > -1)
{
e.Handled = true;
}
}
回答7:
Put this code in textbox_keypress here txtweight is my textbox name you use yours
private void txtweight_KeyPress(object sender, KeyPressEventArgs e) {
if (txtweight.Text.Length == 0)
{
if (e.KeyChar == '.')
{
e.Handled = true;
}
}
if (!char.IsDigit(e.KeyChar) && e.KeyChar != 8 && e.KeyChar != 46)
{
e.Handled = true;
}
if (e.KeyChar == '.' && txtweight.Text.IndexOf('.') > -1)
{
e.Handled = true;
}
}
来源：https://stackoverflow.com/questions/14313810/allow-only-one-decimal-point-in-a-text-box