I am seeing lots of these in a method in our code:
int num1 = 0;
if (Char.IsDigit(myStr[2]) && Int32.TryParse(myStr[2].ToString(), out num1) == false)
{
valid = false;
}
So are they just making sure the third character us a digit?
The code shown parses the 3rd character only - checking if it is digit, then parsing the string representation of that single character. Instead, just use the numeric value of that character:
if(myStr[2] >= '0' && myStr[2] <= '9') {
num1 = (int)myStr[2] - (int)'0';
} else {
valid = false
}
You can safely skip the IsDigit() check as it's redundant.
TryParse() will fail if it's not a digit.
As it has been pointed out by others, Char.IsDigit() is quicker. If your code is performance sensitive the check makes sense.
If you leave the IsDigit check in place, then you can reduce TryParse to Int32.Parse() as at that point the parsing won't fail.
It looks like the code that you have is doing this for efficiency. Whoever coded this, knows the structure of the string in myStr to sometimes have a non-numeric symbol in the third position. That's why he made this optimization to check the third symbol before paying for the conversion of the character array to string which then gets parsed.
Chances are, this optimization is premature: although making a temporary throw-away string is not free, this optimization would make sense only in situations when you do it a lot in a very tight loop. In other words, you do it only if it shows up near the top in your performance profiler's output.
You can optimize this check to avoid if:
int num1 = 0;
valid &= !Char.IsDigit(myStr[2]) || Int32.TryParse(myStr[2].ToString(), out num1);
I don't believe you need the first part (it could also throw an IndexOutOfRangeException).
So I would probably use:
int num1 = 0;
if (myStr.Length > 2 && Int32.TryParse(myStr[2].ToString(), out num1) == false)
{
valid = false;
}
Char.IsDigit Method (String, Int32)
Indicates whether the character at the specified position in a specified string is categorized as a decimal digit.
Link
Int32.TryParse Method
Converts the string representation of a number to its 32-bit signed integer equivalent. A return value indicates whether the operation succeeded. This member is overloaded.
Link
Edit:
First I wrote that you can skip any of the check but now I am writing that you can not because
if (Char.IsDigit(myStr[2]) && Int32.TryParse(myStr[2].ToString(), out num1) == false)
{ }
Char.IsDigit() will return true if myStr[2] contains any of the Unicode characters listed here but Int.TryParse() will not convert any numbers except for 0-9 (not sure about this, as I have not checked all of them) so it will return false which is you are checking...
The condition you are checking can be understood by the following example:
string x = "AS௭s";
int s = 0;
if (Char.IsDigit(x[2]) && int.TryParse(x[2].ToString(), out s) == false)
{
// even if '௭` is Tamil Digit Seven and 'Char.IsDigit()' will return true but
// int.TryParse() will return false because it can not convert it
// so you are setting valid = false when the myStr contains a valid Unicode Character
// for a digit but It can not be converted to integer by TryParse method...
valid = false;
}
#Marc Gravell♦'s answer is the best solution for checking this condition...
Here's how I'd write it:
int num1 = 0;
try
{
num1 = Int32.Parse(myStr[2].ToString());
}
catch (Exception)
{
valid = false;
}
This does the same thing and is a lot easier to read imho, oh & you can log failed parses inside the catch.
Or you can do:
int num1 = 0;
valid = Int32.TryParse(myStr[2].ToString(), out num1);
Related
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;
}
I want to get result of a value with if condition.
i have get some value in xml file.
now what I want is
if I have a variable "a" here i have assigned some values by using dataset.
and i have another variable "b" is assigned value from xml file.
for example
int a=25;
string b=">10"
now I want to check the condition if condition with out ">" because the symbol present in b variable. I dont know how to check this condition can anybody explain me how to acheive this.
I tried like this but not working
if(a+b)
You can use the DataTable.Compute-"trick" to evaulate such expressions:
int a = 25;
string b = ">10";
bool isTrue = (bool)new DataTable().Compute($"{a}{b}", null); // true
What is supported you can read at the DataColumn.Expression remarks.
if the condition is 1!=10, how to use not equal in this code .this
condition is not working what should i do.
As the documentation tells you that is not valid syntax, you have to use <> (look at operators). So a simple approach would be either to use <> in the first place or replace them:
b = b.Replace("!=", "<>");
You can have some function to remove non numeric characters:
public int Parse(string x)
{
x = Regex.Replace(x, "[^0-9.]", "");
int result = 0;
int.TryParse(x , out result);
return result;
}
If its always a number with a symbol then:
symbol = b[0];
int bval = int.Parse(b.Substring(1))
And considering your comment for comparison you can do:
if((symbol=='>'&&a>b)||
(symbol=='='&&a==b)||
(symbol=='<'&&a<b)
){
//do your magic here
}
Of course you may need only one of < = > or you may need to have separate if conditions for each, what ever suits your needs, but I just wanted to give the idea.
I tried like this
if (b.Contains(">")) {
b = b.Replace(">", "");
if (a >Convert.ToInt32(b))
{
Console.WriteLine("value is less");
}
else
{
Console.WriteLine("value is Greater");
}
}
similarly all the symbols
First separate symbol from b:
string symbol = b[0].ToString();
string numberString = b.SubString(1);
int number = int.Parse(numberString);
Now use switch to get operation for symbol and compare:
bool result = false;
switch (symbol)
{
case ">":
if (a > number)
{
result = true;
}
break;
}
EDIT: Changed symbol declaration to avoid error: "cannot implicit convert type char to string"
I need to compare 2 strings using a For without using String.compare. (It's a homework ... I started programming C# 2 weeks ago)
I just can't figure out how to use the for loop to answer the question. I don't know what to put in for(). I tried for( string text1 = "something",) but I can't figure out what toput after the, in the for loop.
Since this is a homework question, I would recommend stop reading the answer as soon as you think you have enough information to solve it on your own before getting to the solution at the end.
Let's assume a simple method signature, first:
public static bool AreStringEqual(string str1, string str2)
{
}
And our goal is to implement (write the code for) this method. We'll assume our goal is Return true if the strings are equal, and return false if they are not. We won't do anything fancy like make it case insensitive.
We can do some basic checks on our strings, first. If they are of different length, then we can immediately assume the strings are different, and return false:
if (str1.Length != str2.Length)
{
return false;
}
This block checks the length, and if they differ, then false is immediately returned and the rest of the method doesn't get executed.
At this point we can guarantee the strings are the same length, so we can loop over the strings and compare them character by character using a for loop.
for(int counter = 0; counter < str1.Length; counter++)
{
}
This is a pretty standard for-loop that just counts a number from zero to one less than the length of the string. It doesn't matter if we use str1 or str2 for the upper bound of the loop since we already know they are the same length.
To get the character in a string, we can use the Indexer Syntax to get the character at a give position. The numbers start at zero in C# and .NET.
str1[0] gets the first character, str1[1] gets the second, etc.
We can then plug the variable in the for loop into the indexer for str1 and str2, then compare the characters. If they are not equal, then return false.
for(int counter = 0; counter < str1.Length; counter++)
{
if (str1[counter] != str2[counter])
{
return false;
}
}
And finally, if the code gets through the for loop without returning false, then return true at the end. Putting it all together, it looks like this:
public static bool AreStringEqual(string str1, string str2)
{
if (str1.Length != str2.Length)
{
return false;
}
for(int counter = 0; counter < str1.Length; counter++)
{
if (str1[counter] != str2[counter])
{
return false;
}
}
return true;
}
I am total noob regarding regex.
My goal is to check whether a string is a valid representation of a hex number.
Currently my implementation (which I find really inefficient) is having a List with all hex digits (0-9, A-F) and checking whether my string contains characters not contained in given List.
I bet this can be easily done using regular expressions but I have no idea how to implement it.
private bool ISValidHEX(string s)
{
List<string> ToCheck = new List<string>();
for (int i = 0; i < 10; i++)
{
ToCheck.Add(i.ToString());
}
ToCheck.Add("A");
ToCheck.Add("B");
ToCheck.Add("C");
ToCheck.Add("D");
ToCheck.Add("E");
ToCheck.Add("F");
for (int i = 0; i < s.Length; i++)
{
if( !ToCheck.Contains(s.Substring(i,1)))
{
return false;
}
}
return true;
}
I would have thought that it's quickest to attempt to convert your string to an integral type and deal with any exception. Use code like this:
int num = Int32.Parse(s, System.Globalization.NumberStyles.HexNumber);
The resulting code is possibly easier to follow than a regular expression and is particularly useful if you need the parsed value (else you could use Int32.TryParse which is adequately documented in other answers).
(One of my favourite quotations is by Jamie Zawinski: "Some people, when confronted with a problem, think 'I know, I'll use regular expressions.' Now they have two problems.")
To simply check
Check if string is valid represantion of HEX number
you may use a method like:
int res = 0;
if(int.TryParse(val,
System.Globalization.NumberStyles.HexNumber,
System.Globalization.CultureInfo.InvariantCulture, out res)) {
//IT'S A VALID HEX
}
Pay attention on System.Globalization.CultureInfo.InvariantCulture parameter, change it according to your needs.
I recommend to use Int32.TryParse.
There is an overload that allow the Hex numbers conversion
int v;
string test = "FF";
if(Int32.TryParse(test, NumberStyles.HexNumber, CultureInfo.CurrentCulture, out v))
Console.WriteLine("Is HEX:" + v.ToString());
This is better than a simple Int32.Parse because, in the case that you have an invalid hex or the conversion overflows the Int32.MaxValue you don't get an exception but you could simply test the boolean return value.
Warning, the string cannot be prefixed with "0x" or "&H"
I tried Google search. I found lots of solutions. Here are two:
Validate Hex Color Code with Regular Expression
Regular Expression Hexadecimal Number Validation
Example
//use System.Text.RegularExpressions before using this function
public bool vldRegex(string strInput)
{
//create Regular Expression Match pattern object
Regex myRegex = new Regex("^[a-fA-F0-9]+$");
//boolean variable to hold the status
bool isValid = false;
if (string.IsNullOrEmpty(strInput))
{
isValid = false;
}
else
{
isValid = myRegex.IsMatch(strInput);
}
//return the results
return isValid;
}
^[0-9a-fA-F]+$ will match strings which are numbers and valid hex letters BUT this doesn't match the possible 0x at the front. I'm sure you can add that if needed.
If your hex string will have a maximum of 32 characters (e.g. usually GUIDs fit this bill), then you could PadLeft the string with zeros to ensure it has always 32 characters and then use the Guid.TryParse
public static bool IsHex(string hexString)
{
var isHex = false;
if ((hexString ?? string.Empty).Length == 0)
return false;
if (hexString.Length > 0 && hexString.Length <= 32)
{
hexString = hexString.PadLeft(32, '0');
Guid guid;
isHex = Guid.TryParse(hexString, out guid);
}
else
{
throw new NotImplementedException("Use some other way to check the hex string!");
}
return isHex;
}
Try it here:
https://dotnetfiddle.net/bLaCAT
I need to check if a string contains only digits. How could I achieve this in C#?
string s = "123" → valid
string s = "123.67" → valid
string s = "123F" → invalid
Is there any function like IsNumeric?
double n;
if (Double.TryParse("128337.812738", out n)) {
// ok
}
works assuming the number doesn't overflow a double
for a huge string, try the regexp:
if (Regex.Match(str, #"^[0-9]+(\.[0-9]+)?$")) {
// ok
}
add in scientific notation (e/E) or +/- signs if needed...
Taken from MSDN (How to implement Visual Basic .NET IsNumeric functionality by using Visual C#):
// IsNumeric Function
static bool IsNumeric(object Expression)
{
// Variable to collect the Return value of the TryParse method.
bool isNum;
// Define variable to collect out parameter of the TryParse method. If the conversion fails, the out parameter is zero.
double retNum;
// The TryParse method converts a string in a specified style and culture-specific format to its double-precision floating point number equivalent.
// The TryParse method does not generate an exception if the conversion fails. If the conversion passes, True is returned. If it does not, False is returned.
isNum = Double.TryParse(Convert.ToString(Expression), System.Globalization.NumberStyles.Any, System.Globalization.NumberFormatInfo.InvariantInfo, out retNum );
return isNum;
}
You can use double.TryParse
string value;
double number;
if (Double.TryParse(value, out number))
Console.WriteLine("valid");
else
Console.WriteLine("invalid");
This should work no matter how long the string is:
string s = "12345";
bool iAllNumbers = s.ToCharArray ().All (ch => Char.IsDigit (ch) || ch == '.');
Using regular expressions is the easiest way (but not the quickest):
bool isNumeric = Regex.IsMatch(s,#"^(\+|-)?\d+(\.\d+)?$");
As stated above you can use double.tryParse
If you don't like that (for some reason), you can write your own extension method:
public static class ExtensionMethods
{
public static bool isNumeric (this string str)
{
for (int i = 0; i < str.Length; i++ )
{
if ((str[i] == '.') || (str[i] == ',')) continue; //Decide what is valid, decimal point or decimal coma
if ((str[i] < '0') || (str[i] > '9')) return false;
}
return true;
}
}
Usage:
string mystring = "123456abcd123";
if (mystring.isNumeric()) MessageBox.Show("The input string is a number.");
else MessageBox.Show("The input string is not a number.");
Input :
123456abcd123
123.6
Output:
false
true
I think you can use Regular Expressions, in the Regex class
Regex.IsMatch( yourStr, "\d" )
or something like that off the top of my head.
Or you could use the Parse method int.Parse( ... )
If you are receiving the string as a parameter the more flexible way would be to use regex as described in the other posts.
If you get the input from the user, you can just hook on the KeyDown event and ignore all keys that are not numbers. This way you'll be sure that you have only digits.
This should work:
bool isNum = Integer.TryParse(Str, out Num);