TheDeveloperBlog.com


C# Loop Over String Chars

Loop over string chars. A loop iterates over individual string characters. It allows processing for each char. The foreach-loop and the for-loop are available for this purpose. The string indexer returns a char value.

Indexer

Example. First, we look at two loops where we iterate over each char in a string. The string you loop over can be a string literal, a variable, or a constant. We use the foreach and for-loop.

C# program that uses foreach on string

using System;

class Program
{
    static void Main()
    {
	const string s = "peace";
	foreach (char c in s)
	{
	    Console.WriteLine(c);
	}
	for (int i = 0; i < s.Length; i++)
	{
	    Console.WriteLine(s[i]);
	}
    }
}

Output

p
e
a
c
e

p
e
a
c
e


Performance. For performance, it is sometimes easier for the JIT compiler to optimize the loops if you do not hoist the Length check outside of the for-loop. It is not often helpful to store the length in a local variable.

JIT

StringBuilder. For long inputs where we build up an output, a StringBuilder is important. It means we don't have to worry about hundreds or thousands of appends happening in edge cases.

StringBuilderStringBuilder Performance

Regex. Sometimes using a loop is far more efficient than a Regex. Another advantage of loops is the ability to test each character and alert the user to special characters. Loops are imperative and offer more control.

However: Regular expressions offer more power in fewer characters. They are sometimes a better option.

Regex Versus LoopRegex.Match

Summary. This simple method loops over each character in a string. The performance here is good because it only needs to make one pass over the string. Often, we use loops to test for special patterns.

Tip: You can find a benchmark of different ways to loop over strings with the for-loop in the C# language on this site.

String For-Loop