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I am following a c# course and trying to upgrade my user input method to check if the entered console input is an integer. I have written myself into a do while loop that I know doesn't work, but I am struggling a bit with coming up with a method that can both check for value and if the entered variable is an integer.
So what I tried here was to do-while until the user entered input is an Integer and between the min and max values. But I get stuck on result is only set to a value in the 'if' block, not the 'else' block. It won't compile unless result is set to something, unassigned variable. And I understand why, because there is a branch where I end up with a variable without value, and that won't pass in my while greater-less comparisson. You can only compare numbers, not nulls or strings.
Should I abandon the do-while loop for something more clever? Right now my 'hack' is to set result = 0 in the case that TryParse is false.
That is only useful as long as the user does not need to input 0, in which case the whole thing makes no sense any longer.
static int readInt(string prompt, int low, int high) // METHOD readInt
{
int result;
bool succes;
do
{
int temp;
string intString = readString(prompt);
succes = Int32.TryParse(intString, out temp);
if (succes)
{ Console.WriteLine("The string was a number within the limits, {0}.", intString);
result = int.Parse(intString);
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
result = 0;
}
} while (!succes && (result < low) || (result > high));
return result;
}
It might be easier to just use a while (true) loop and return from inside the loop when you have a valid result. This is a structured construct known as a loop with one exit, so it's fine to use (if you're worried about structured programming).
For example:
static int readInt(string prompt, int low, int high) // METHOD readInt
{
while (true)
{
string intString = readString(prompt);
if (Int32.TryParse(intString, out var result) && (result >= low) && (result <= high))
{
Console.WriteLine("The string was a number within the limits, {0}.", intString);
return result;
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
}
}
}
Note the use of a relatively recent C# feature, the ability to declare an out variable at the point of use using the var keyword - see the out var result inside the TryParse().
Or for a simpler pattern
int result;
string intString;
while (!int.TryParse(intString = Console.ReadLine(), out result) || result < low || result > high)
Console.WriteLine($"{intString} is not a valid number between {low} and {high}");
Console.WriteLine("The string was a number within the limits, {result}.");
return result;
you can change your " result = int.Parse(intString);" in the "if" with "return temp";
you already have the number from your TryParse, so you do not need to parse it again; returning inside the "if" also removes the need to assign a value to 'result' inside the "else" in fact, you don't need "result" at all)
static int readInt(string prompt, int low, int high) // METHOD readInt
{
bool succes;
do
{
string intString = readString(prompt);
succes = Int32.TryParse(intString, out int temp);
if (succes)
{ Console.WriteLine("The string was a number within the limits, {0}.", intString);
return temp;
}
else
{
Console.WriteLine("{0} is not a valid number between {1} and {2}", intString, low, high);
}
} while (!succes && (result < low) || (result > high));
}
You had a couple of bugs in the code. This works:
static int readInt(int low, int high)
{
int result;
bool success;
bool outOfLimits = false;
do
{
Console.Write("Enter a number: ");
string intString = Console.ReadLine();
success = Int32.TryParse(intString, out result);
if (!success)
{
Console.WriteLine("{0} is not a valid number.", intString, low, high);
continue;
}
outOfLimits = result < low || result > high;
if (outOfLimits)
Console.WriteLine("The string was NOT a number between {1} and {2}.", intString, low, high);
else
Console.WriteLine("The string was a number within the limits, {0}.", intString);
} while (!success || outOfLimits);
return result;
}
When code evolves like yours, it sometimes gets a bit unclear what it does as the complexity rises. Usually that's a sign that you should refactor it.
I would try to make the code clearer by moving all the checks for validity into a method by itself. Then you can do something like this.
static int readInt(string prompt, int low, int high) // METHOD readInt
{
bool valid = false;
int result = 0;
while (!valid)
{
var intString = readString(prompt);
valid = checkIfValid(intString, low, high, out result);
}
return result;
}
static bool checkIfValid(string s, int low, int high, out int result)
{
if (!Int32.TryParse(s, out result))
{
Console.WriteLine(s + " isn't an integer");
return false;
}
if (result < low)
{
Console.WriteLine("Number is too low");
return false;
}
if (result > high)
{
Console.WriteLine("Number is too high");
return false;
}
return true;
}
Try implementing the routine validating the conditions one after one (we have no need to make code too complex with !succes && (result < low) || (result > high) check):
If user input a valid integer (int.TryParse)?
If valid is it within the range?
If any validation fails keep asking user:
static int readInt(string prompt, int low, int high)
{
// Keep on looping until we return a valid result
while (true)
{
// Or
// Console.WriteLine(prompt);
// string input = Console.ReadLine();
string input = readString(prompt);
int result = 0; // initialization: let the compiler be happy
if (!int.TryParse(input, out result)) // Do we have an syntactically invalid input?
Console.WriteLine($"{input} is not a valid integer number");
else if (result < low || result > high) // If result is valid; is it out of range?
Console.WriteLine($"{input} is out of [{low}..{high}] range");
else // result is valid integer and within the ranges: time to return it
return result;
}
}
I have public string method with an if/else statement. When I don't put a return keyword on the else, I get the error that not all code paths return a value but when I add the return to the else statement, I get an Use of unassigned local variable 'result'. When I do return "Please enter a valid number";, nothing displays on the console when I type in any letter. I need to let the user know that they entered something in that couldn't be converted into an integer.
public string AddNumbers(string userInputString)
{
int result;
int num2 = RandomNumberInt();
bool isTrue = int.TryParse(userInputString, out int num1);
if (isTrue == true)
{
result = num1 + num2;
Console.WriteLine("Adding your number and a random number, please wait...");
Thread.Sleep(1000);
Console.WriteLine("{0} + {1} = {2}", num1, num2, result);
isTrue = true;
return result.ToString();
}
else
{
return "Please enter a valid number";
}
}
It's because your method is asking for a return. But since you have an if, let's put it this way
Team Leader: Hey bob I want you to finish this job.
In here you are expecting that bob will finish your job but you put a condition
You: If I can go to office today sir.
since you have an If condition, what if you can't go today? Does it mean you can't finish the job tomorrow and any other day? That's why it says not all code paths return a value because you never gave other/default value
Going back in your code, you ask
if (isTrue == true)
{
result = num1 + num2;
Console.WriteLine("Adding your number and a random number, please wait...");
Thread.Sleep(1000);
Console.WriteLine("{0} + {1} = {2}", num1, num2, result);
isTrue = true;
return result.ToString();
}
but what if it is not true, then it will go to else. You can set int result = 0 so it is defined from start when else run and it will not return an error of unassigned local variable.
public string myMethod()
{
int result = 0; //This must have a default value so in else part it is not unassigned when you return.
int num2 = RandomNumberInt();
bool isTrue = int.TryParse(userInputString, out int num1);
if(isTrue)
{
//do something in result here
return result.toString(); //This will return your in value as string
}
else
{
return "Your message as string" // This will return any string to provide for string return of the method
}
}
Your problem regarding not displaying the string "Please enter a valid number" is a different issue. You have to post also what method calls the AddNumbers method that will use the returned string. For use the problem is in that method because your if and else is in correct format;
Whenever you get confused by application logic, it is often helpful to break the logic down into pieces. This gives you an opportunity to think through the problem and decide how the tasks add up to give you the final result.
Start at a high level and sketch out the overall flow:
static public void MethodNameThatDescribesThisActivity()
{
var userResponse = ReadIntegerFromConsole("Please enter an integer.");
var randomNumber = RandomNumberInt();
DisplaySum(userResponse, randomNumber, 1000);
}
Then implement the pieces:
static public int ReadIntegerFromConsole(string prompt)
{
int result;
while (true)
{
Console.WriteLine(prompt);
var input = Console.ReadLine();
var ok = int.TryParse(input, out result);
if (ok) break;
Console.WriteLine("That isn't a valid integer.");
}
return result;
}
static public void DisplaySum(int userNumber, int randomNumber, int delay)
{
var sum = userNumber + randomNumber;
Thread.Sleep(delay);
Console.WriteLine("The total of {0} + {1} = {2}", userNumber, randomNumber, sum);
}
If you do it this way, it often solves the logic problem for you. And it also makes your code easier to read.
I am trying to check if a textbox contains a number. The problem is that it always returns that it contains a non-numeric character.
I've tried several ways, but none of them seems to work.
One of the ways I've tried is:
if( Regex.IsMatch(tb.Text.Trim(), #"^[0-9]+$")) // tb.Text is the textbox
It does not matter what I enter in the textbox, it always returns that it contains a non-numeric character (I tried entering 1-9, 'a', 'b')
You could just parse the string to a specific number type, i.e.
double result;
if (!double.TryParse(tb.Text, out result))
{
//text is not a valid double;
throw new Exception("not a valid number");
}
//else the value is within the result variable
From your regex it seems that you need only integer values, so you should use int.TryParse or long.TryParse instead.
Quick and dirty test program:
void Main()
{
TestParse("1");
TestParse("a");
TestParse("1234");
TestParse("1a");
}
void TestParse(string text)
{
int result;
if (int.TryParse(text, out result))
{
Console.WriteLine(text + " is a number");
}
else
{
Console.WriteLine(text + " is not a number");
}
}
Results:
1 is a number
a is not a number
1234 is a number
1a is not a number
You could replace your Regex for this:
if(Regex.IsMatch(tb.Text.Trim(), #"[0-9]"))
Or for this:
if(Regex.IsMatch(tb.Text.Trim(), #"\d"))
you can use TryParse:
int value;
bool IsNumber = int.TryParse(tb.Text.Trim(), out value);
if(IsNumber)
{
//its number
}
private void btnMove_Click(object sender, EventArgs e)
{
string check = txtCheck.Text;
string status = "";
for (int i = 0; i < check.Length; i++)
{
if (IsNumber(check[i]))
status+="The char at "+i+" is a number\n";
}
MessageBox.Show(status);
}
private bool IsNumber(char c)
{
return Char.IsNumber(c);
}
I'd like to know on C# how to check if a string is a number (and just a number).
Example :
141241 Yes
232a23 No
12412a No
and so on...
Is there a specific function?
Look up double.TryParse() if you're talking about numbers like 1, -2 and 3.14159. Some others are suggesting int.TryParse(), but that will fail on decimals.
string candidate = "3.14159";
if (double.TryParse(candidate, out var parsedNumber))
{
// parsedNumber is a valid number!
}
EDIT: As Lukasz points out below, we should be mindful of the thread culture when parsing numbers with a decimal separator, i.e. do this to be safe:
double.TryParse(candidate, NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out var parsedNumber)
If you just want to check if a string is all digits (without being within a particular number range) you can use:
string test = "123";
bool allDigits = test.All(char.IsDigit);
Yes there is
int temp;
int.TryParse("141241", out temp) = true
int.TryParse("232a23", out temp) = false
int.TryParse("12412a", out temp) = false
Hope this helps.
Use Int32.TryParse()
int num;
bool isNum = Int32.TryParse("[string to test]", out num);
if (isNum)
{
//Is a Number
}
else
{
//Not a number
}
MSDN Reference
Use int.TryParse():
string input = "141241";
int ouput;
bool result = int.TryParse(input, out output);
result will be true if it was.
Yep - you can use the Visual Basic one in C#.It's all .NET; the VB functions IsNumeric, IsDate, etc are actually static methods of the Information class. So here's your code:
using Microsoft.VisualBasic;
...
Information.IsNumeric( object );
int value;
if (int.TryParse("your string", out value))
{
Console.WriteLine(value);
}
This is my personal favorite
private static bool IsItOnlyNumbers(string searchString)
{
return !String.IsNullOrEmpty(searchString) && searchString.All(char.IsDigit);
}
Perhaps you're looking for the int.TryParse function.
http://msdn.microsoft.com/en-us/library/system.int32.tryparse.aspx
Many datatypes have a TryParse-method that will return true if it managed to successfully convert to that specific type, with the parsed value as an out-parameter.
In your case these might be of interest:
http://msdn.microsoft.com/en-us/library/system.int32.tryparse.aspx
http://msdn.microsoft.com/en-us/library/system.decimal.tryparse.aspx
int result = 0;
bool isValidInt = int.TryParse("1234", out result);
//isValidInt should be true
//result is the integer 1234
Of course, you can check against other number types, like decimal or double.
You should use the TryParse method for the int
string text1 = "x";
int num1;
bool res = int.TryParse(text1, out num1);
if (res == false)
{
// String is not a number.
}
If you want to validate if each character is a digit and also return the character that is not a digit as part of the error message validation, then you can loop through each char.
string num = "123x";
foreach (char c in num.ToArray())
{
if (!Char.IsDigit(c))
{
Console.WriteLine("character " + c + " is not a number");
return;
}
}
int.TryPasrse() Methode is the best way
so if the value was string you will never have an exception , instead of the TryParse Methode return to you bool value so you will know if the parse operation succeeded or failed
string yourText = "2";
int num;
bool res = int.TryParse(yourText, out num);
if (res == true)
{
// the operation succeeded and you got the number in num parameter
}
else
{
// the operation failed
}
string str = "123";
int i = Int.Parse(str);
If str is a valid integer string then it will be converted to integer and stored in i other wise Exception occur.
Starting with C# 7.0, you can declare the out variable in the argument
list of the method call, rather than in a separate variable
declaration. This produces more compact, readable code, and also
prevents you from inadvertently assigning a value to the variable
before the method call.
bool isDouble = double.TryParse(yourString, out double result);
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/out-parameter-modifier
You could use something like the following code:
string numbers = "numbers you want to check";
Regex regex = new Regex("^[0-9]+$"));
if (regex.IsMatch(numbers))
{
//string value is a number
}
public static void Main()
{
string id = "141241";
string id1 = "232a23";
string id2 = "12412a";
validation( id, id1, id2);
}
public static void validation(params object[] list)
{
string s = "";
int result;
string _Msg = "";
for (int i = 0; i < list.Length; i++)
{
s = (list[i].ToString());
if (string.IsNullOrEmpty(s))
{
_Msg = "Please Enter the value";
}
if (int.TryParse(s, out result))
{
_Msg = "Enter " + s.ToString() + ", value is Integer";
}
else
{
_Msg = "This is not Integer value ";
}
}
}
Try This
here i perform addition of no and concatenation of string
private void button1_Click(object sender, EventArgs e)
{
bool chk,chk1;
int chkq;
chk = int.TryParse(textBox1.Text, out chkq);
chk1 = int.TryParse(textBox2.Text, out chkq);
if (chk1 && chk)
{
double a = Convert.ToDouble(textBox1.Text);
double b = Convert.ToDouble(textBox2.Text);
double c = a + b;
textBox3.Text = Convert.ToString(c);
}
else
{
string f, d,s;
f = textBox1.Text;
d = textBox2.Text;
s = f + d;
textBox3.Text = s;
}
}
I'm not a programmer of particularly high skills, but when I needed to solve this, I chose what is probably a very non-elegant solution, but it suits my needs.
private bool IsValidNumber(string _checkString, string _checkType)
{
float _checkF;
int _checkI;
bool _result = false;
switch (_checkType)
{
case "int":
_result = int.TryParse(_checkString, out _checkI);
break;
case "float":
_result = Single.TryParse(_checkString, out _checkF);
break;
}
return _result;
}
I simply call this with something like:
if (IsValidNumber("1.2", "float")) etc...
It means that I can get a simple true/false answer back during If... Then comparisons, and that was the important factor for me. If I need to check for other types, then I add a variable, and a case statement as required.
use this
double num;
string candidate = "1";
if (double.TryParse(candidate, out num))
{
// It's a number!
}
int num;
bool isNumeric = int.TryParse("123", out num);
namespace Exception
{
class Program
{
static void Main(string[] args)
{
bool isNumeric;
int n;
do
{
Console.Write("Enter a number:");
isNumeric = int.TryParse(Console.ReadLine(), out n);
} while (isNumeric == false);
Console.WriteLine("Thanks for entering number" + n);
Console.Read();
}
}
}
Regex.IsMatch(stringToBeChecked, #"^\d+$")
Regex.IsMatch("141241", #"^\d+$") // True
Regex.IsMatch("232a23", #"^\d+$") // False
Regex.IsMatch("12412a", #"^\d+$") // False
The problem with some of the suggested solutions is that they don't take into account various float number formats. The following function does it:
public bool IsNumber(String value)
{
double d;
if (string.IsNullOrWhiteSpace(value))
return false;
else
return double.TryParse(value.Trim(), System.Globalization.NumberStyles.Any,
System.Globalization.CultureInfo.InvariantCulture, out d);
}
It assumes that the various float number styles such es decimal point (English) and decima comma (German) are all allowed. If that is not the case, change the number styles paramater. Note that Any does not include hex mumbers, because the type double does not support it.
I have heard that using exception trapping is not a recommended practice for number testing.
For example:
bool isnumeric
try
{
int i = int.parse(textbox1.text);
isnumeric = true;
}
catch {isnumenric=false}
Is there some other way that I could test for numbers in C#?
Yes try using
int i;
bool success = Int32.TryParse(textBox1.text, out i);
The TryParse method basically does what you are doing above.
Use the built-in TryParse
E.g.
int number;
bool result = Int32.TryParse(value, out number);
Yes. Use int.TryParse, double.TryParse, etc. instead, which all return a boolean.
Alternately, there's an IsNumeric function buried in the VB assemblies (in the Microsoft.VisualBasic namespace in Microsoft.VisualBasic.dll) that you can also call from your C# code:
bool Microsoft.VisualBasic.Information.IsNumeric(value)
TryParse()
int i;
if(Int32.TryParse(someString,out i))
{
//now use i because you know it is valid
//otherwise, TryParse would have returned false
}
int result = -1;
bool isNumeric = Int32.TryParse(text, out result);
isNumeric will be true if the number is numeric, false otherwise; if the number is numeric, result will have the numeric value of the number.
bool TryParse(string, out int)
It will return a bool that is true if it was able to parse the integer, and the out parameter will contain the integer (if it was successful with the parsing).
If you just need to do number testing and do not need the integer number, you may use the function below. This is faster than Int32.TryParse(...) methods.
Edit for Barry Fandango: Handles negative numbers now. This is only for testing integers.
public static bool IsNumber(string s)
{
if (s == null || s.Length == 0)
{
return false;
}
if (s[0] == '-')
{
for (int i = 1; i < s.Length; i++)
{
if (!char.IsDigit(s[i]))
{
return false;
}
}
}
else
{
foreach (char c in s)
{
if (!char.IsDigit(c))
{
return false;
}
}
}
return true;
}
If you want the integer then Int32.TryParse(...) is what you want else
Information.IsNumeric(...) (From the Microsoft.VisualBasic.dll) if you don't care what the actual integer is.