#100 – Using IndexOf to Search for Characters Within A String
September 25, 2010 2 Comments
You can search for the following within a string:
- A single character
- One of a set of characters
- A substring
You search for a single character in a string using the String.IndexOf method, which returns a 0-based index into the string.
string s = "Thomas Paine";
int n = s.IndexOf('a'); // 4 (1st 'a')
You can also specify a starting position for the search. So we can find the next occurrence of ‘a’ this way:
n = s.IndexOf('a', n+1); // 8 (start search after 1st 'a')
You can search for the first occurrence of one of a set of characters using the IndexOfAny method.
string s = "Thomas Paine";
char[] vowels = new char[] {'a','e','i','o','u'};
int n = s.IndexOfAny(vowels); // 2
n = s.IndexOfAny(vowels, n + 1); // 4
You can also use IndexOf to search for substrings within a string.
string s = "A man, a plan, a canal";
int n = s.IndexOf("an"); // 3
n = s.IndexOf("an", n + 1); // 11
About Sean
2,000 Things You Should Know About C# 
I’m teaching myself C# for a new job and just wanted to say thanks for putting all of these together. I’ve found them very useful.
Typo: “use IndexOf so search” → ‘use IndexOf to search’