So I'm doing this years Advent of Code and I'm stuck on the second day, part 2.
You are given inputs which look like this:
"1-3 c: caaasa"
You have to check how many passwords are valid due to the policy like,
in above example:
letter c has to be in position 1 OR 3 in the string caaasa. If
yes, the password is valid.
I've broken down that string to different sections, and now I try to compare a string "znak" which contains that given letter to a letter on position zakresmin and zakresmax in string "passdiv"
Yet, everytime it returns False, so it doesn't add up to the count of passwords.
I tried using Equals() and CompareTo(), but they don't seem to work.
How can I modify my code so it returns proper values?
var iloschasel = 0;
using (StreamReader sr = new StreamReader(#"C:\Users\Wurf\Desktop\text.txt"))
{
string line;
while ((line = sr.ReadLine()) != null)
{
string[] linia = line.Split(" ");
string zakres = linia[0];
string[] zakresy = zakres.Split("-");
int zakresmin = Convert.ToInt32(zakresy[0]);
int zakresmax = Convert.ToInt32(zakresy[1]);
string znak = (linia[1].Replace(":", "")).Trim();
var suma = Regex.Matches(linia[2], znak);
string passdiv = linia[2];
if(passdiv[zakresmin].Equals(znak) || passdiv[zakresmax - 1].Equals(znak))
{
iloschasel += 1;
}
}
}
Console.WriteLine(iloschasel);
As mentioned, when you call Equals on two different types you are playing a game of chance with how the actual types are implemented. In this case you lose. Strings and chars will never have an equivalence or the same reference.
I believe the compiler or resharper would give you a warning alerting you that neither type derive from string and char
However, I was bored enough to give an alternate solution
public static bool IsValid(string input)
{
var match = Regex.Match(input, #"(\d)-(\d) (\S): (.*)");
if(!match.Success)
throw new ArgumentException( $"Invalid format : {input}",nameof(input));
var first = int.Parse(match.Groups[1].Value);
var second = int.Parse(match.Groups[2].Value);
var c = char.Parse(match.Groups[3].Value);
var password = match.Groups[4].Value;
return password[first-1] == c && password[second-1] == c;
}
Test
Console.WriteLine($"Is Valid = {IsValid("1-3 c: caaasa")}");
Console.WriteLine($"Is Valid = {IsValid("1-3 c: cacaasa")}");
Output
Is Valid = False
Is Valid = True
Note : this is not meant to be a complete bullet-proof solution. Just a novel elegant way to solve your problem
Your problem is that you are comparing a string to a char
var match = "c" == 'c';
Will give a compile error because they are different data types
var match = "c".Equals('c');
will let you compile, but will always return false because a char will never equal a string. You have to turn the char into a string or visa versa for the check to work
var match = "c"[0] == 'c';
So in your if statement, if you fix the check to compare strings with strings or chars with chars you should get some positive results. And also fix your indexing issue to decide if you want a 0 based index or a 1 based index with zakresmin and max
Also as a side note, it can be helpful to step through your code line by line in debug mode, to find out which line isn't behaving like you expect it to. In your case debugging would have helped you zero in on the if statement as a starting point to fixing things.
So it turns out (if I understand that correctly) that a compared element of the string passdiv was a char which I tried to compare to znak which was a string. I added ToString() to my code and it works well. Also fixed the range of zakresmin by subtracting 1 so it works properly.
if((passdiv[zakresmin - 1].ToString() == znak && passdiv[zakresmax - 1].ToString() != znak) || (passdiv[zakresmin - 1].ToString() != znak && passdiv[zakresmax - 1].ToString() == znak))
{
iloschasel += 1;
}
If I have these strings:
"abc" = false
"123" = true
"ab2" = false
Is there a command, like IsNumeric() or something else, that can identify if a string is a valid number?
int n;
bool isNumeric = int.TryParse("123", out n);
Update As of C# 7:
var isNumeric = int.TryParse("123", out int n);
or if you don't need the number you can discard the out parameter
var isNumeric = int.TryParse("123", out _);
The var s can be replaced by their respective types!
This will return true if input is all numbers. Don't know if it's any better than TryParse, but it will work.
Regex.IsMatch(input, #"^\d+$")
If you just want to know if it has one or more numbers mixed in with characters, leave off the ^ + and $.
Regex.IsMatch(input, #"\d")
Edit:
Actually I think it is better than TryParse because a very long string could potentially overflow TryParse.
You can also use:
using System.Linq;
stringTest.All(char.IsDigit);
It will return true for all Numeric Digits (not float) and false if input string is any sort of alphanumeric.
Test case
Return value
Test result
"1234"
true
✅Pass
"1"
true
✅Pass
"0"
true
✅Pass
""
true
⚠️Fail (known edge case)
"12.34"
false
✅Pass
"+1234"
false
✅Pass
"-13"
false
✅Pass
"3E14"
false
✅Pass
"0x10"
false
✅Pass
Please note: stringTest should not be an empty string as this would pass the test of being numeric.
I've used this function several times:
public static bool IsNumeric(object Expression)
{
double retNum;
bool isNum = Double.TryParse(Convert.ToString(Expression), System.Globalization.NumberStyles.Any, System.Globalization.NumberFormatInfo.InvariantInfo, out retNum);
return isNum;
}
But you can also use;
bool b1 = Microsoft.VisualBasic.Information.IsNumeric("1"); //true
bool b2 = Microsoft.VisualBasic.Information.IsNumeric("1aa"); // false
From Benchmarking IsNumeric Options
(source: aspalliance.com)
(source: aspalliance.com)
This is probably the best option in C#.
If you want to know if the string contains a whole number (integer):
string someString;
// ...
int myInt;
bool isNumerical = int.TryParse(someString, out myInt);
The TryParse method will try to convert the string to a number (integer) and if it succeeds it will return true and place the corresponding number in myInt. If it can't, it returns false.
Solutions using the int.Parse(someString) alternative shown in other responses works, but it is much slower because throwing exceptions is very expensive. TryParse(...) was added to the C# language in version 2, and until then you didn't have a choice. Now you do: you should therefore avoid the Parse() alternative.
If you want to accept decimal numbers, the decimal class also has a .TryParse(...) method. Replace int with decimal in the above discussion, and the same principles apply.
You can always use the built in TryParse methods for many datatypes to see if the string in question will pass.
Example.
decimal myDec;
var Result = decimal.TryParse("123", out myDec);
Result would then = True
decimal myDec;
var Result = decimal.TryParse("abc", out myDec);
Result would then = False
In case you don't want to use int.Parse or double.Parse, you can roll your own with something like this:
public static class Extensions
{
public static bool IsNumeric(this string s)
{
foreach (char c in s)
{
if (!char.IsDigit(c) && c != '.')
{
return false;
}
}
return true;
}
}
If you want to catch a broader spectrum of numbers, à la PHP's is_numeric, you can use the following:
// From PHP documentation for is_numeric
// (http://php.net/manual/en/function.is-numeric.php)
// Finds whether the given variable is numeric.
// Numeric strings consist of optional sign, any number of digits, optional decimal part and optional
// exponential part. Thus +0123.45e6 is a valid numeric value.
// Hexadecimal (e.g. 0xf4c3b00c), Binary (e.g. 0b10100111001), Octal (e.g. 0777) notation is allowed too but
// only without sign, decimal and exponential part.
static readonly Regex _isNumericRegex =
new Regex( "^(" +
/*Hex*/ #"0x[0-9a-f]+" + "|" +
/*Bin*/ #"0b[01]+" + "|" +
/*Oct*/ #"0[0-7]*" + "|" +
/*Dec*/ #"((?!0)|[-+]|(?=0+\.))(\d*\.)?\d+(e\d+)?" +
")$" );
static bool IsNumeric( string value )
{
return _isNumericRegex.IsMatch( value );
}
Unit Test:
static void IsNumericTest()
{
string[] l_unitTests = new string[] {
"123", /* TRUE */
"abc", /* FALSE */
"12.3", /* TRUE */
"+12.3", /* TRUE */
"-12.3", /* TRUE */
"1.23e2", /* TRUE */
"-1e23", /* TRUE */
"1.2ef", /* FALSE */
"0x0", /* TRUE */
"0xfff", /* TRUE */
"0xf1f", /* TRUE */
"0xf1g", /* FALSE */
"0123", /* TRUE */
"0999", /* FALSE (not octal) */
"+0999", /* TRUE (forced decimal) */
"0b0101", /* TRUE */
"0b0102" /* FALSE */
};
foreach ( string l_unitTest in l_unitTests )
Console.WriteLine( l_unitTest + " => " + IsNumeric( l_unitTest ).ToString() );
Console.ReadKey( true );
}
Keep in mind that just because a value is numeric doesn't mean it can be converted to a numeric type. For example, "999999999999999999999999999999.9999999999" is a perfeclty valid numeric value, but it won't fit into a .NET numeric type (not one defined in the standard library, that is).
I know this is an old thread, but none of the answers really did it for me - either inefficient, or not encapsulated for easy reuse. I also wanted to ensure it returned false if the string was empty or null. TryParse returns true in this case (an empty string does not cause an error when parsing as a number). So, here's my string extension method:
public static class Extensions
{
/// <summary>
/// Returns true if string is numeric and not empty or null or whitespace.
/// Determines if string is numeric by parsing as Double
/// </summary>
/// <param name="str"></param>
/// <param name="style">Optional style - defaults to NumberStyles.Number (leading and trailing whitespace, leading and trailing sign, decimal point and thousands separator) </param>
/// <param name="culture">Optional CultureInfo - defaults to InvariantCulture</param>
/// <returns></returns>
public static bool IsNumeric(this string str, NumberStyles style = NumberStyles.Number,
CultureInfo culture = null)
{
double num;
if (culture == null) culture = CultureInfo.InvariantCulture;
return Double.TryParse(str, style, culture, out num) && !String.IsNullOrWhiteSpace(str);
}
}
Simple to use:
var mystring = "1234.56789";
var test = mystring.IsNumeric();
Or, if you want to test other types of number, you can specify the 'style'.
So, to convert a number with an Exponent, you could use:
var mystring = "5.2453232E6";
var test = mystring.IsNumeric(style: NumberStyles.AllowExponent);
Or to test a potential Hex string, you could use:
var mystring = "0xF67AB2";
var test = mystring.IsNumeric(style: NumberStyles.HexNumber)
The optional 'culture' parameter can be used in much the same way.
It is limited by not being able to convert strings that are too big to be contained in a double, but that is a limited requirement and I think if you are working with numbers larger than this, then you'll probably need additional specialised number handling functions anyway.
UPDATE of Kunal Noel Answer
stringTest.All(char.IsDigit);
// This returns true if all characters of the string are digits.
But, for this case we have that empty strings will pass that test, so, you can:
if (!string.IsNullOrEmpty(stringTest) && stringTest.All(char.IsDigit)){
// Do your logic here
}
You can use TryParse to determine if the string can be parsed into an integer.
int i;
bool bNum = int.TryParse(str, out i);
The boolean will tell you if it worked or not.
If you want to know if a string is a number, you could always try parsing it:
var numberString = "123";
int number;
int.TryParse(numberString , out number);
Note that TryParse returns a bool, which you can use to check if your parsing succeeded.
I guess this answer will just be lost in between all the other ones, but anyway, here goes.
I ended up on this question via Google because I wanted to check if a string was numeric so that I could just use double.Parse("123") instead of the TryParse() method.
Why? Because it's annoying to have to declare an out variable and check the result of TryParse() before you know if the parse failed or not. I want to use the ternary operator to check if the string is numerical and then just parse it in the first ternary expression or provide a default value in the second ternary expression.
Like this:
var doubleValue = IsNumeric(numberAsString) ? double.Parse(numberAsString) : 0;
It's just a lot cleaner than:
var doubleValue = 0;
if (double.TryParse(numberAsString, out doubleValue)) {
//whatever you want to do with doubleValue
}
I made a couple extension methods for these cases:
Extension method one
public static bool IsParseableAs<TInput>(this string value) {
var type = typeof(TInput);
var tryParseMethod = type.GetMethod("TryParse", BindingFlags.Static | BindingFlags.Public, Type.DefaultBinder,
new[] { typeof(string), type.MakeByRefType() }, null);
if (tryParseMethod == null) return false;
var arguments = new[] { value, Activator.CreateInstance(type) };
return (bool) tryParseMethod.Invoke(null, arguments);
}
Example:
"123".IsParseableAs<double>() ? double.Parse(sNumber) : 0;
Because IsParseableAs() tries to parse the string as the appropriate type instead of just checking if the string is "numeric" it should be pretty safe. And you can even use it for non numeric types that have a TryParse() method, like DateTime.
The method uses reflection and you end up calling the TryParse() method twice which, of course, isn't as efficient, but not everything has to be fully optimized, sometimes convenience is just more important.
This method can also be used to easily parse a list of numeric strings into a list of double or some other type with a default value without having to catch any exceptions:
var sNumbers = new[] {"10", "20", "30"};
var dValues = sNumbers.Select(s => s.IsParseableAs<double>() ? double.Parse(s) : 0);
Extension method two
public static TOutput ParseAs<TOutput>(this string value, TOutput defaultValue) {
var type = typeof(TOutput);
var tryParseMethod = type.GetMethod("TryParse", BindingFlags.Static | BindingFlags.Public, Type.DefaultBinder,
new[] { typeof(string), type.MakeByRefType() }, null);
if (tryParseMethod == null) return defaultValue;
var arguments = new object[] { value, null };
return ((bool) tryParseMethod.Invoke(null, arguments)) ? (TOutput) arguments[1] : defaultValue;
}
This extension method lets you parse a string as any type that has a TryParse() method and it also lets you specify a default value to return if the conversion fails.
This is better than using the ternary operator with the extension method above as it only does the conversion once. It still uses reflection though...
Examples:
"123".ParseAs<int>(10);
"abc".ParseAs<int>(25);
"123,78".ParseAs<double>(10);
"abc".ParseAs<double>(107.4);
"2014-10-28".ParseAs<DateTime>(DateTime.MinValue);
"monday".ParseAs<DateTime>(DateTime.MinValue);
Outputs:
123
25
123,78
107,4
28.10.2014 00:00:00
01.01.0001 00:00:00
If you want to check if a string is a number (I'm assuming it's a string since if it's a number, duh, you know it's one).
Without regex and
using Microsoft's code as much as possible
you could also do:
public static bool IsNumber(this string aNumber)
{
BigInteger temp_big_int;
var is_number = BigInteger.TryParse(aNumber, out temp_big_int);
return is_number;
}
This will take care of the usual nasties:
Minus (-) or Plus (+) in the beginning
contains decimal character BigIntegers won't parse numbers with decimal points. (So: BigInteger.Parse("3.3") will throw an exception, and TryParse for the same will return false)
no funny non-digits
covers cases where the number is bigger than the usual use of Double.TryParse
You'll have to add a reference to System.Numerics and have
using System.Numerics; on top of your class (well, the second is a bonus I guess :)
Double.TryParse
bool Double.TryParse(string s, out double result)
The best flexible solution with .net built-in function called- char.IsDigit. It works with unlimited long numbers. It will only return true if each character is a numeric number. I used it lot of times with no issues and much easily cleaner solution I ever found. I made a example method.Its ready to use. In addition I added validation for null and empty input. So the method is now totally bulletproof
public static bool IsNumeric(string strNumber)
{
if (string.IsNullOrEmpty(strNumber))
{
return false;
}
else
{
int numberOfChar = strNumber.Count();
if (numberOfChar > 0)
{
bool r = strNumber.All(char.IsDigit);
return r;
}
else
{
return false;
}
}
}
Try the regex define below
new Regex(#"^\d{4}").IsMatch("6") // false
new Regex(#"^\d{4}").IsMatch("68ab") // false
new Regex(#"^\d{4}").IsMatch("1111abcdefg")
new Regex(#"^\d+").IsMatch("6") // true (any length but at least one digit)
With c# 7 it you can inline the out variable:
if(int.TryParse(str, out int v))
{
}
Use these extension methods to clearly distinguish between a check if the string is numerical and if the string only contains 0-9 digits
public static class ExtensionMethods
{
/// <summary>
/// Returns true if string could represent a valid number, including decimals and local culture symbols
/// </summary>
public static bool IsNumeric(this string s)
{
decimal d;
return decimal.TryParse(s, System.Globalization.NumberStyles.Any, System.Globalization.CultureInfo.CurrentCulture, out d);
}
/// <summary>
/// Returns true only if string is wholy comprised of numerical digits
/// </summary>
public static bool IsNumbersOnly(this string s)
{
if (s == null || s == string.Empty)
return false;
foreach (char c in s)
{
if (c < '0' || c > '9') // Avoid using .IsDigit or .IsNumeric as they will return true for other characters
return false;
}
return true;
}
}
public static bool IsNumeric(this string input)
{
int n;
if (!string.IsNullOrEmpty(input)) //.Replace('.',null).Replace(',',null)
{
foreach (var i in input)
{
if (!int.TryParse(i.ToString(), out n))
{
return false;
}
}
return true;
}
return false;
}
Regex rx = new Regex(#"^([1-9]\d*(\.)\d*|0?(\.)\d*[1-9]\d*|[1-9]\d*)$");
string text = "12.0";
var result = rx.IsMatch(text);
Console.WriteLine(result);
To check string is uint, ulong or contains only digits one .(dot) and digits
Sample inputs
123 => True
123.1 => True
0.123 => True
.123 => True
0.2 => True
3452.434.43=> False
2342f43.34 => False
svasad.324 => False
3215.afa => False
Hope this helps
string myString = "abc";
double num;
bool isNumber = double.TryParse(myString , out num);
if isNumber
{
//string is number
}
else
{
//string is not a number
}
Pull in a reference to Visual Basic in your project and use its Information.IsNumeric method such as shown below and be able to capture floats as well as integers unlike the answer above which only catches ints.
// Using Microsoft.VisualBasic;
var txt = "ABCDEFG";
if (Information.IsNumeric(txt))
Console.WriteLine ("Numeric");
IsNumeric("12.3"); // true
IsNumeric("1"); // true
IsNumeric("abc"); // false
All the Answers are Useful. But while searching for a solution where the Numeric value is 12 digits or more (in my case), then while debugging, I found the following solution useful :
double tempInt = 0;
bool result = double.TryParse("Your_12_Digit_Or_more_StringValue", out tempInt);
Th result variable will give you true or false.
Here is the C# method.
Int.TryParse Method (String, Int32)
bool is_number(string str, char delimiter = '.')
{
if(str.Length==0) //Empty
{
return false;
}
bool is_delimetered = false;
foreach (char c in str)
{
if ((c < '0' || c > '9') && (c != delimiter)) //ASCII table check. Not a digit && not delimeter
{
return false;
}
if (c == delimiter)
{
if (is_delimetered) //more than 1 delimiter
{
return false;
}
else //first time delimiter
{
is_delimetered = true;
}
}
}
return true;
}
My Goal: Extracting one value from an Excel Range, and verify for these cells' value to be the same within this range;
When a cell's value is not the same as the other, I need to return null.
Here's a piece of code:
internal object GetValueFromCells(string start, string end, Formats format) {
// Verifying for empty or null parameters here and throwing accordingly...
try {
Range cells = Excel.get_Range(start, end) as Range;
object value = null;
bool sameValue = false;
foreach(Range cell in cells) {
// This condition block shall execute only once, since 'value' shall not be null afterwards.
if (value == null || value == DBNull.Value)
if (Formats.Formated == format) {
value = cell.Text;
// The following results to be false !?...
sameValue = value == cell.Text; // Shall this not be true?
} else {
value = cell.Value2;
// The following results to be false !?...
sameValue = value == cell.Value2; // Shall this not be true?
}
// This results being always false!?...
// Shall this not be true, I wonder?
sameValue = Formats.Formated == format ? value == cell.Text : value == cell.Value2;
if(!sameValue)
return null;
}
return value;
} catch (Exception ex) {
// Exception handling...
}
}
Reading this code, I would humbly expect a value to be returned when all of the cells in the range have the same value (for instance 334).
However, this methods always returns null (Nothing in Visual Basic)!
Anyone might explain what I'm missing here while this:
value == cell.Value2
always returns false?
Perhaps is it my algorithm that isn't quite right?
EDIT #1
This has solved the problem:
sameValue = Formats.Formatted == format ? cell.Text.Equals(value) : cell.Value2.Equals(value);
I accepted #Jerod Houghtelling's answer as his answer suggests both the ToString() and the Equals() methods to solve the problem.
In addition to it, I dislike having to call the ToString() method, since the value can be numbers, and comparing numbers under a string looks odd to me. So I prefer the Equals() way which I adopted within my solution.
I would like to thank #Sir Gallahad and #Jerod Houghtelling for their good answers. This was the first time I had to face such a situation, and they both helped me better understand what was going on under the hood, plus the others who contributed too through comments.
And thanks to those who upvoted my question. This serves a purpose to demonstrate that I was not so dumb asking! =P Hehehe...
I'm guessing that cell.Value2 is returning a new instance of an object each time you call it. Therefore I would deduce the == is checking to see if both sides of the equation are the same instance of the object. To actually compare the value stored on both side you will have to use the .Equals or convert the values to something that can be compared, for example a string.
sameValue = value.Equals( cell.Value2 );
/* or */
sameValue = value.ToString() == cell.Value2.ToString();
Also I don't see value being set in your example.
Probably the value == cell.Value2 are comparing objects that are from different instances.
Try value.ToString() == cell.Value2.ToString()