 Let's have a look at this, finding and replacing characters and substrings inside of strings. Now remember the variable we had before, str underscore r, let's just have a look at what it was again. It says this is going to be a fairly extended sentence. Now let's look at this in function. It's going to look for specific characters, it can look for specific characters inside of a string. So in takes the following arguments, what you're looking for and you see the single quotation marks I'm looking for character and inside of this computer variable str underscore r which is the string, this is going to be a fairly long sentence and it just returns true. It could find an f inside of that string. So in helps just for Boolean returns but let's use this contains function. Now for contains we're going to look for strings, now just watch out, the order of these arguments are the other way around now, so it contains the string that I'm looking for and the string inside of that string I'm looking for, so I'm asking is fairly inside of that string of mine and indeed it's true, it's right there. Now let's look at the search function, so there's quite a few of these and don't get confused between them, keep these notes handy. So note the f is in double quotation marks here, so search which is the same order of these arguments as the contains, so the string I'm looking for and f which is now double quotation marks. So there we go it says it found an f, it found only one in position 25, so remember the index of a string in position 25. Now let's do the following, instead of just looking for an f I'm now doing a search but I'm doing it on this array of characters, it's characters because I'm using single quotation marks, let's see what happens there, it just returns one value, now this is going to be a fairly long sentence, where do I have it, this is going to be a fairly long or fairly extended sentence, so certainly there are g's in there, there's an i in there, there's an f in there, but it just looks down that array and it looks for the first thing that it can find, and in position three there was an i for this, in this, there we go an i there, so it's the first thing it finds out of that array it's going to return to us. Let's just do this search again just on this string and now we're going to put a whole string inside of it and it says yes it found fairly and it took the index from 25 to 30, a bit of regular expressions using search and I said we're going to get to that, I'll explain to you what this is all about, it says this is a regular expression, anything that has it starts with an f and this dot here is just for anything that follows, it's like kind of like a wild card and that means right to the end, so the first if it found was a 25 and then everything after that was included. I'll get to exactly what all of this means you needn't have put that but it will get to all of that. Now replacing substrings or characters using the replace function, so I can say replace inside of my string the word fairly because we know now it's there with the word very, let's see what that is, this is going to be a very extended sentence, I can also replace it with an uppercase, so there's I'm going to take the string I'm going to replace fairly with its uppercase equivalent, so there's going to be a fairly extended sentence. Now note what happens now, if I were just to call the string again even though I've changed it it's still the same, it is still the same, the very which we replaced it with and then the fairly which was capital is gone because strings are what we call immutable, they cannot be changed after we've created them, so there's no replace with this bang, this exclamation mark, so that certainly does not exist, so you'll have to create a new version of that string and you copy of that string if you've changed it. Next up and that is the last section in this lesson is the very exciting world of regular expressions.