How string quote, length total count and arrayname[int] work?

Question

I'm making a program which reverses words to sdrow.

I understand that for it to work it needs to be written this way. I'm more interested on WHY it has to be this way.

Here is my code:

 Console.WriteLine("Enter a word : ");
 string word = Console.ReadLine();
 string rev = "";
 int length;

 for (length = word.Length - 1; length >= 0; length--)
 {
     rev = rev + word[length];
 }

 Console.WriteLine("The reversed word is : {0}", rev);

My questions are:

a) why you must use quotes to initialize your string

b) Why must you start your loop at one less than the total length of your string

c) How arrayname[int] works

I'm pretty new to C# and this site, as well. I hope my questions make sense and that I've asked them in the correct and proper way.

Thank you for your time!

Answer 1

This is how I've interpreted your question.

1. You want to know why you must use quotes to initialize your string
2. Why must you start your loop at one less than the total length of your string
3. How arrayname[int] works

I think that the best way to explain this to you is to go through your code, and explain what it does.

Console.WriteLine("Enter a word : ");

The first line of code prints Enter a word : into the console.

string word = Console.ReadLine();

This line "reads" the input from the console, and puts it into a string called word.

string rev = "";

This initiates a string called rev, setting it's value to "", or an empty string. The other way to initiate the string would be this:

string rev;

That would initiate a string called rev to the value of null. This does not work for your program because rev = rev + word[length]; sets rev to itself + word[length]. It throws an error if it is null.

The next line of your code is:

int length;

That sets an int (which in real life we call an integer, basically a number) to the value of null. That is okay, because it gets set later on without referencing itself.

The next line is a for loop:

for (length = word.Length - 1; length >= 0; length--)

This loop sets an internal variable called length to the current value of word.Length -1. The second item tells how long to run the loop. While the value of length is more than, or equal to 0, the loop will continue to run. The third item generally sets the rate of increase or decrease of your variable. In this case, it is length-- that decreases length by one each time the loop runs.

The next relevant line of code is his:

rev = rev + word[length];

This, as I said before sets rev as itself + the string word at the index of length, whatever number that is at the time.

At the first run through the for loop, rev is set to itself (an empty string), plus the word at the index of length - 1. If the word entered was come (for example), the index 0 would be c, the index 1 would be o, 2 would be m, and 3 = e.

The word length is 4, so that minus one is 3 (yay - back to Kindergarten), which is the last letter in the word.

The second time through the loop, length will be 2, so rev will be itself (e) plus index 2, which is m. This repeats until length hits -1, at which point the loop does not run, and you go on to the next line of code.

...Which is:

Console.WriteLine("The reversed word is : {0}", rev);

This prints a line to the console, saying The reversed word is : <insert value of rev here> The {0} is an internal var set by the stuff after the comma, which in this case would be rev.

The final output of the program, if you inserted come, would look something like this:

>Enter a word :  
>come
>
>The reversed word is : emoc

Answer 2

a) you must to initialize or instantiate the variable in order to can work with it. In your case is better to use and StringBuilder, the string are inmutable objects, so each assignement means to recreate a new string.

b) The arrays in C# are zero index based so their indexes go from zero to length -1.

c) An string is an characters array.

Any case maybe you must to try the StringBuilder, it is pretty easy to use

I hope this helps

Answer 3

a) you need to initialize a variable if you want to use it in an assignment rev = rev + word[length];

b) you are using a for loop which means that you define a start number length = word.Length - 1, a stop criteria length >= 0 and a variable change length--

So lenght basically descends from 5 to 0 (makes 6 loops). The reason is that Arrays like 'string' a char[] are zerobased indexed.. means that first element is 0 last is array.Length - 1

c) So a string is basically a chain of char's.. with the []-Operator you can access a single index. The Return Type of words[index] is in this case a character.

I hope it helped

Answer 4

a) You need to first instantiate the string rev before you can assign it values in the loop. You could also say "string rev = String.Empty". You are trying to add word to rev and if you don't tell it first that rev is an empty string it doesn't know what it is adding word to.

b) The characters of the string have indexes to show which position they appear in the string. These indexes start at 0. So you're first character will have an index of 0. If the length of your string is 6 then the last character's index will be 5. So length - 1 will give you the value of the last character's index which is 5. A c# for loop uses the following parameters

for (int i = 0; i < 10; i++)
    {
        Console.WriteLine(i);
    }

where "int i = 0;" is the starting index; "i < 10" tells the loop when to stop looping; and "i++" tells it to increment i (the index) after each loop. So in your code you are saying start at the last character of my string; perform this loop while there are still characters in the string; and decrease the index of the string after each loop so the next loop will look at the previous character in the string.

c) word[length] then in this scenario is saying add the character that has the position with index "length" to the rev string. This will basically reverse the word.

Answer 5

As usual you can do it in linq and avoid the (explicit) loops

using System;
using System.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Enter a word : ");
            string word = Console.ReadLine();

            Console.WriteLine("The reversed word is : {0}", new string (word.Reverse().ToArray()));
            Console.ReadLine();
        }
    }
}

Answer 6

var reversedWords = string.Join(" ",
      str.Split(' ')
         .Select(x => new String(x.Reverse().ToArray())));

Take a look here :

Easy way to reverse each word in a sentence