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C# Change Characters in StringModify many characters in a string at once using ToCharArray and a for-loop.
Change characters. In C# programs, strings are immutable. If we want to change their characters, we must first convert them to arrays.
C# performance. A char array can be changed in memory before conversion back to a string. This is efficient. We show how to change string characters in this way.
Char Array
Input and output. Consider the string "eee 123." We may wish to make 2 separate changes in it at once—change the letter, and the whitespace.
Required output:
INPUT: eee 123 OUTPUT: uuu-123
Example code. We use a series of if-statements to change characters in a string. You can make many mutations in a single pass through the string.
Next We make 3 changes: we lowercase characters, and we change the values of spaces and one letter.
ToCharArray This method will cause an allocation upon the managed heap. Then, the new string constructor will allocate another string.
ToCharArray
Info Compared to making multiple changes with ToLower and Replace, this approach saves allocations.
ToLower
Replace
Tip This will reduce memory pressure and ultimately improve runtime performance.
C# program that changes characters in string
using System; class Program { static void Main() { string input = "eee 123"; // Change uppercase to lowercase. // Change space to hyphen. // Change e to u. char[] array = input.ToCharArray(); for (int i = 0; i < array.Length; i++) { char let = array[i]; if (char.IsUpper(let)) { array[i] = char.ToLower(let); } else if (let == ' ') { array[i] = '-'; } else if (let == 'e') { array[i] = 'u'; } } string result = new string(array); Console.WriteLine(result); } }
uuu-123
ROT13. Some transformations are not possible using standard string methods. ROT13 encoding is best done with the ToCharArray and new string constructor style of code.
ROT13
One letter. If you need to change one letter at a certain position (such as the first letter), this approach to string mutation is also ideal.
Uppercase First Letter
String Constructor
Summary. To change chars in a string, you must use a lower-level representation of the character data, which you can acquire with ToCharArray. You cannot simply assign indexes in a string.
Summary, continued. This style of method introduces complexity. It is often best to wrap this logic in a helper method, and call that method.
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