Develop Reference

Is there any method in C# like equalsIgnoreCase from Java

I'm new to C# I came from a Java background, I'm trying to find a method to compare 2 strings if they are equal but to the ignore case.
In Java you can type somthing like this
boolean equal = "abc".equalsIgnoreCase("ABC");
is there anything like that in C# ?. I know that I can use
var equal = String.Compare("abc", "ABC", StringComparison.OrdinalIgnoreCase);
or
var equal = String.Equals("abc", "ABC", StringComparison.InvariantCultureIgnoreCase);
I just want to know if there is anything shorter (without having to pass a StringComparison Enum )

you can create an extension method:
internal static class StringExtensions
{
public static bool EqualsIgnoreCase(this string str1, string str2)
{
return String.Equals(str1, str2, StringComparison.InvariantCultureIgnoreCase);
}
}
Then use it this way: bool equals = "abc".EqualsIgnoreCase("ABC");

if (true) Shorthand

Is there a shorthand when checking a boolean for true?
Example:
if (autoConnect) Connect();
We can do
return IsOpen() ? true : false;
But I cant get
autoConnect ? Connect();
running. Is there a way to do this?

You could write an extension method:
public static void _(this bool b, Action ifTrue)
{
if (b) { ifTrue(); }
}
then you could write:
autoConnect._(Connect);
although obviously this is not very readable and is not recommended.

The only thing you can shorten is to remove the conditional operator:
return IsOpen() ? true : false;
and just
return IsOpen();

No, no way to get autoConnect ? Connect(); working.
just return the bool value, don't need a ternary operator:
return IsOpen();
Alternativelly, you return some values when a value you want to test can be null using the ?? operator, for sample:
return a ?? b;
If a is null, then return b.

To answer your question, no, there is no shorthand to make
if (autoConnect) Connect();
any shorter. Also, your proposed solution only saves up 3 characters, which is an unnecessary golfing of otherwise perfectly readable code.

As siride says if (autoConnect) Connect(); is the shortest way. Altough, this is just while writing code. Whenever the compiler compiles the code it will become the same as using if (autoConnect) { Connect(); } or if (autoConnect == true) { Connect(); }.
You should use whatever you find the most clean or easiest reading.

string to bool inline conversion

What I currently have:
bool okPress = !string.IsNullOrEmpty(Ctx.Request["okPress"]) &&
Convert.ToBoolean(Ctx.Request["okPress"]);
Correct me if I'm wrong here, but wouldn't this throw a FormatException if the string isn't "true/True" or "false/False"? Is there any way to handle the conversion in one row, without having to worry about exceptions? Or do I need to use Boolean.TryParse?

You can use Boolean.TryParse:
bool okPress;
bool success = Boolean.TryParse(Ctx.Request["okPress"]), out okPress);
For what it's worth, here a "one-liner", create following extension which might be useful especially in LINQ queries:
public static bool TryGetBool(this string item)
{
bool b;
Boolean.TryParse(item, out b);
return b;
}
and write:
bool okPress = Ctx.Request["okPress"].TryGetBool();

IF you didn't want to use TryParse You could do something like
bool okPress = !string.IsNullOrEmpty(Ctx.Request["okPress"]) &&
(Ctx.Request["okPress"].ToLower()=="true");
This way if the string is not true/false it will just assume false for you with no exceptions thrown.
This does of course assume that you are happy for a value of "fish" to be treated as false rather than as an exception.
Better though is to just not do it as a single line. You don't generally have a maximum number of lines of code so two or three simple lines of code are often better than one complicated line of code...

Why don't you compare the string against true?
bool okPress = !string.IsNullOrEmpty(Ctx.Request["okPress"]) &&
String.Compare(Ctx.Request["okPress"], "true", StringComparison.OrdinalIgnoreCase) == 0

You can use TryParse method of Boolean class as you said.
Tries to convert the specified string representation of a logical
value to its Boolean equivalent. A return value indicates whether the
conversion succeeded or failed.
bool result = Boolean.TryParse(Ctx.Request["okPress"]), out okPress);
It returns true if value was converted successfully; otherwise, false.

Your inline conversion.
public static bool TryParseAsBoolean(this string expression)
{
bool booleanValue;
bool.TryParse(expression, out booleanValue);
return booleanValue;
}
bool okPress = Ctx.Request["okPress"].TryParseAsBoolean();

Null and blank values

What's the best way of writing robust code so that a variable can be checked for null and blank.
e.g.
string a;
if((a != null) && (a.Length() > 0))
{
//do some thing with a
}

For strings, there is
if (String.IsNullOrEmpty(a))

You can define an extension method to allow you to do this on many things:
static public bool IsNullOrEmpty<T>(this IEnumerable <T>input)
{
return input == null || input.Count() == 0;
}
It already exists as a static method on the System.String class for strings, as has been pointed out.

And if you are using .NET 4.0 you might want to take a look at String.IsNullOrWhiteSpace.

From version 2.0 you can use IsNullOrEmpty.
string a;
...
if (string.IsNullOrEmpty(a)) ...

if(string.IsNullOrEmpty(string name))
{
/// write ur code
}

for strings:
string a;
if(!String.IsNullOrEmpty(a))
{
//do something with a
}
for specific types you could create an extention method
note that i've used HasValue instead of IsNullorEmpty because 99% of the times you will have to use the !-operator if you use IsNullOrEmpty which I find quite unreadable
public static bool HasValue(this MyType value)
{
//do some testing to see if your specific type is considered filled
}

I find Apache Commons.Lang StringUtils (Java)'s naming a lot easier: isEmpty() checks for null or empty string, isBlank() checks for null, empty string, or whitespace-only. isNullOrEmpty might be more descriptive, but empty and null is, in most cases you use it, the same thing.

Is there a C# case insensitive equals operator?

I know that the following is case sensitive:
if (StringA == StringB) {
So is there an operator which will compare two strings in an insensitive manner?

Try this:
string.Equals(a, b, StringComparison.CurrentCultureIgnoreCase);

The best way to compare 2 strings ignoring the case of the letters is to use the String.Equals static method specifying an ordinal ignore case string comparison. This is also the fastest way, much faster than converting the strings to lower or upper case and comparing them after that.
I tested the performance of both approaches and the ordinal ignore case string comparison was more than 9 times faster! It is also more reliable than converting strings to lower or upper case (check out the Turkish i problem). So always use the String.Equals method to compare strings for equality:
String.Equals(string1, string2, StringComparison.OrdinalIgnoreCase);
If you want to perform a culture specific string comparison you can use the following code:
String.Equals(string1, string2, StringComparison.CurrentCultureIgnoreCase);
Please note that the second example uses the the string comparison logic of the current culture, which makes it slower than the "ordinal ignore case" comparison in the first example, so if you don't need any culture specific string comparison logic and you are after maximum performance, use the "ordinal ignore case" comparison.
For more information, read the full story on my blog.

There are a number of properties on the StringComparer static class that return comparers for any type of case-sensitivity you might want:
StringComparer Properties
For instance, you can call
StringComparer.CurrentCultureIgnoreCase.Equals(string1, string2)
or
StringComparer.CurrentCultureIgnoreCase.Compare(string1, string2)
It's a bit cleaner than the string.Equals or string.Compare overloads that take a StringComparison argument.

System.Collections.CaseInsensitiveComparer
or
System.StringComparer.OrdinalIgnoreCase

string.Equals(StringA, StringB, StringComparison.CurrentCultureIgnoreCase);

or
if (StringA.Equals(StringB, StringComparison.CurrentCultureIgnoreCase)) {
but you need to be sure that StringA is not null. So probably better tu use:
string.Equals(StringA , StringB, StringComparison.CurrentCultureIgnoreCase);
as John suggested
EDIT: corrected the bug

You can use
if (stringA.equals(StringB, StringComparison.CurrentCultureIgnoreCase))

Operator? NO, but I think you can change your culture so that string comparison is not case-sensitive.
// you'll want to change this...
System.Threading.Thread.CurrentThread.CurrentCulture
// and you'll want to custimize this
System.Globalization.CultureInfo.CompareInfo
I'm confident that it will change the way that strings are being compared by the equals operator.

Here an idea to simplify the syntax:
public class IgnoreCase
{
private readonly string _value;
public IgnoreCase(string s)
{
_value = s;
}
protected bool Equals(IgnoreCase other)
{
return this == other;
}
public override bool Equals(object obj)
{
return obj != null &&
(ReferenceEquals(this, obj) || (obj.GetType() == GetType() && this == (IgnoreCase) obj));
}
public override int GetHashCode()
{
return _value?.GetHashCode() ?? 0;
}
public static bool operator ==(IgnoreCase a, IgnoreCase b)
{
return string.Equals(a, b, StringComparison.OrdinalIgnoreCase);
}
public static bool operator !=(IgnoreCase a, IgnoreCase b)
{
return !(a == b);
}
public static implicit operator string(IgnoreCase s)
{
return s._value;
}
public static implicit operator IgnoreCase(string s)
{
return new IgnoreCase(s);
}
}
Usable like:
Console.WriteLine((IgnoreCase) "a" == "b"); // false
Console.WriteLine((IgnoreCase) "abc" == "abC"); // true
Console.WriteLine((IgnoreCase) "Abc" == "aBc"); // true
Console.WriteLine((IgnoreCase) "ABC" == "ABC"); // true

I am so used to typing at the end of these comparison methods: , StringComparison.
So I made an extension.
namespace System
{ public static class StringExtension
{
public static bool Equals(this string thisString, string compareString,
StringComparison stringComparison)
{
return string.Equals(thisString, compareString, stringComparison);
}
}
}
Just note that you will need to check for null on thisString prior to calling the ext.

string.Compare(string1, string2, true)

Others answer are totally valid here, but somehow it takes some time to type StringComparison.OrdinalIgnoreCase and also using String.Compare.
I've coded simple String extension method, where you could specify if comparison is case sensitive or case senseless with boolean - see following answer:
https://stackoverflow.com/a/49208128/2338477

if (StringA.ToUpperInvariant() == StringB.ToUpperInvariant()) {
People report ToUpperInvariant() is faster than ToLowerInvariant().

//You can make it case insensitive by
s1.ToLower() == s2.ToLower();