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The ToLower() method of String class is used to convert all the characters in the invoked String to lowercase letters and returns its lowercase form.

Some overloads of ToLower() method

Methods	Description
ToLower()	This method returns a lowercase copy of the invoked String object.
ToLower(CultureInfo)	This method returns a lowercase copy of the invoked String object, by using the casing rule of the specified culture, specified by CultureInfo class.

Note

The ToLower() method when called on any String object, returns a lowercase copy of the invoked String. The returned lowercase String must be stored or used otherwise it is lost.

Calling ToLower() method on a String object.




//Program to convert a String to lowercase letters. 


using System;

class StringUpper
{
public static void Main()
{
	//Creating the first String object
	String str1 = "New Zealand";

	//Creating a char array
	char[] char = {'H', 'E', 'L', 'L', 'O'};

	//Creating the second String object from a char[] array.
	String str2 = new String(char);

	Console.WriteLine("First String is : "+ str1);
	Console.WriteLine("First String's lowercase value : " + str1.ToLower());
	Console.WriteLine("Second String is : "+ str2);
	Console.WriteLine("Second String's lowercase value : " + str2.ToLower());
}
}





Output




First String is : New Zealand
First String's lowercase value : new zealand
Second String is : HELLO
Second String's lowercase value : hello


We have created two String objects, where the first String object was initialized to a value New Zealand, while the second String object was initialized to a value HELLO. When the method ToLower() was called on each of these String object, it returned a lowercase copy of the invoked String object.






Method ToLower() does not modify the original content in a String object


The method ToLower() only returns the content of String object in lowercase letters without modifying its original content at all.


Let's understand this by an example -:
Here in program below, we have initialized a String object with a value new york and we are trying to lowercase all the characters in it by calling ToLower() method on this String object.



//C# Calling method ToLower() does not modify the original content of the invoked String object


using System;

class StringUpper
{
public static void Main()
{
	//Creating a String object
	String str1 = "Mars - The Red Planet";

	//Creating a char array
	char[] arr = {'E', 'a', 'r', 't', 'h'};

	//Creating the second String object from a char[] array.
	String str2 = new String(arr);


	//Printing the value of the first String before calling ToLower() on it
	Console.WriteLine("First string : "+ str1);

	//Printing the lowercase copy of the first String returned by ToLower()
	Console.WriteLine("First String's lowercase value : " + str1.ToLower());

	//Printing the value of the first String after calling ToLower() on it.
	Console.WriteLine("First string after calling ToLower() : " + str1);

	//Printing the value of the second String before calling ToLower() on it
	Console.WriteLine("Second string : "+ str2);

	//Printing the lowercase copy of the second String returned by ToLower()
	Console.WriteLine("Second String's lowercase value : " + str2.ToLower());

	//Printing the value of the second String after calling ToLower() on it.
	Console.WriteLine("Second string after calling ToLower() : " + str2);
}

}





Output is :




First string : Mars - The Red Planet
First String's lowercase value : mars - the red planet
First string after calling ToLower() : Mars - The Red Planet
Second string : Earth
Second String's lowercase value : earth
Second string after calling ToLower() : Earth


Even after calling the method ToLower() on the first String object, the original case of its content remains the same - Mars - The Red Planet, because the method ToLower() only returns the lowercase copy of the invoked String object, without changing the original case of its content and same is the case with the second String object as well.




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ToLower(), by using the casing rules of a specific culture.


A variant of ToLower() method returns a lowercase copy of the invoked String object, by using the casing rule of the specific culture, specified by the CultureInfo class, defined within the System.Globalozation namespace.

To do this, we will call the constructor of the CultureInfo class that accepts a String(representing the culture) and a bool value that specifies whether to use the user-selected culture settings from the system or not.



//C# Calling method ToLower() does not modify the original content of the invoked String object


using System;
using System.Globalization;

class StringUpper
{
public static void Main()
{
	//Creating a String object
	String str1 = "Keep Working Hard For Your Dreams";


	//Printing the value of the first String before calling ToLower() on it
	Console.WriteLine("String : "+ str1);


	//Creating an object of CultureInfo class based on the English-US culture 
	CultureInfo ci1 = new CultureInfo("en-us", false);

	//Creating an object of CultureInfo class based on the Turkish-Turkey culture 
	CultureInfo ci2 = new CultureInfo("tk-TR", false);
	
	//Creating an object of CultureInfo class based on the Turkish-Turkey culture 
	CultureInfo ci3 = new CultureInfo("fr-FR", false);


	//Printing a lowercase copy of the first String according to English-United States culture 
	Console.WriteLine("String's lowercase value based on English-US culture: " + str1.ToLower(ci1));

	//Printing a lowercase copy of the first String according to Turkish-Turkey culture 
	Console.WriteLine("String's lowercase value based on Turkish-Turkish culture: " + str1.ToLower(ci2));

	//Printing a lowercase copy of the first String according to French-France culture 
	Console.WriteLine("String's lowercase value based on French-France culture: " + str1.ToLower(ci3));
	
	
	//Extracting the current culture of our system
	CultureInfo current = CultureInfo.CurrentUICulture;
	Console.WriteLine("The current UI culture of our system is {0}", current.Name);
}

}





Output is :




String : Keep Working Hard For Your Dreams
String's lowercase value based on English-US culture: keep working hard for your dreams
String's lowercase value based on Turkish-Turkish culture: keep working hard for your dreams
String's lowercase value based on French-France culture: keep working hard for your dreams
The current UI culture of our system is en-US


In our last example, we have extracted a lowercase copy of an invoked String object according to different cultures, by using an instance of CultureInfo class passed to a variant of the ToLower() method.






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