Reverse-String.md

Reverse a string

The problem

Reverse a string.

If the input is: Hello World.

The output should be: .dlroW olleH

Hints

A string is almost like a list. A list of characters. You can access any element by index. You can run a for loop on it. You will get each character as an element. Besides, you can also add two string or join two characters

my_string = "You are my Hero"
 
print('Access by index')
print('-------------')
print(my_string[0])
print(my_string[1])
print(my_string[4])
 
print('Run a for loop')
print('-------------')
for char in my_string:
   print(char)
 
print('now join strings')
print('-------------')
print('hello' + 'world')
print('h'+'w')

Try it on Programming Hero

However, a string is not a list.

Give me more: non-premium A string is called an ordered sequence. This means it is an order sequence. That's why you can access a sequence (a position) by an index.

Also, you can run for a loop.

However, a string is not a changeable thing. Sometimes, people refer to the phrase “not changeable” as immutable. Immutable means, it’s not mutable (not changeable).

That’s why you would not be able to append or remove a character from a string. Or you can not set any element by an index.

my_string[3] = ‘c’

This will throw an exception.

In summary, just remember- you can access string by index but you cannot directly set it or change it.

The indirect way is to create a new string and keep adding by the plus sign.

Solution

def reverse_string(str):
   reverse = ""
   for char in str:
       reverse = char + reverse
   return reverse
 
str = input("Enter your string: ")
result = reverse_string(str)
print(result)

Try it on Programming Hero

Explanation

A simple trick will make it work.

Let’s say you wrote “Hello world.” if you break down it or run a for loop and get each character at a time. You will get first H and then e and then l … and so on.

Now, while adding each character add it before the previous one.

Hence, first you will have H. then while adding e, you will add it before the H. It will become eH.

Then “l” will come and add it before. This will give you-

leH

Keep doing it. And you will get

.dlroW olleH

Now if you look at the code you will understand why we did-

reverse = char + reverse

Quiz

What does it mean by the word immutable?

1. Immortal
2. Not changeable
3. Changeable

Show Answer

The answer is: 2

Quiz

Will you be able to append, remove or set a character to string by the index?

1. Yes
2. No
3. Sometimes

Show Answer

The answer is: 2

take Away

A string is an immutable ordered sequence.

   

tags: programmig-hero python float int math