C# third index of a character in a string

Question

is there a command that can get the third index of a character in a string? For example:

error: file.ext: line 10: invalid command [test:)]

Answer 1

int pos = -1;
for ( int k = 0; k < 3; ++k )
{
  pos = s.indexOf( ':', pos+1 );
  // Check if pos < 0...
}