3.2.6 String Handling Operations in a Programming Language

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1 String Handling

String_Handling_Main.png

Learn It: What does string handling mean?

Strings – A string is any sequence of characters from the keyboard, including digits,
letters, punctuation and any other characters you can see when you look at your keyboard.
It is a very important data structure in programming because it is used to achieve many things.
Casting – Converting a piece of data to a specific data type. For example, a user might enter
a string and the program might convert it to an integer in order to perform certain calculations.

Typical operations on strings

  • Because strings are so important, programmers need to know how to carry out a number of frequently used operations on them. These include:
    • Finding the length of a string.
    • Finding the position of a character.
    • Getting a substring (also called a slice) from a string.
    • Concatenation of strings.
    • Converting a character into its ASCII character code.
    • Converting an ASCII character code into a character.
    • Converting digits between string digits and numerical digits.

  • Strings are a useful way of storing any data that you do not need to perform calculations on.
  • However, there are times when you need to be able to select a part of a string, manipulate a string or convert it to another data type.

Learn It: Length

Length:

  • Using the Python code, we can ask the user for a name and then using the LEN function find out the length of the name as follows:

String_LEN.png

  • Entering the name “George” then the LEN function would return “6”.

Learn It: Position

Position

  • Position will find out where in the string a character appears. Don’t forget it will start counting from 0.
  • In this example, it will find the letter “o” in the name and display the number of the position.

String_Pos.png

  • With the name “George” the find function will return “2”.
  • In Python, if the letter cannot be found it will return the value of -1.

Learn It: Substring

Substring

  • A substring is a group of two or more characters that appears inside another string.
  • For instance, “the best of” is a substring of “It was the best of times”.
  • The substring can be found as long as you know the start position and the end position of the string you are looking for.

String_Substring.png

  • Don’t forget Python needs an extra position counted at the end, otherwise it will stop when it reaches the last letter and not show it.
  • This substring will return “ngo”.
  • It is assumed that the start position is 0 and not 1, so message[ 0 ] contains the first character of the string “M”.

Try It: Substrings

  1. Write some pseudocode so that the user types in a message and then they are asked for a letter in that sentence.
  2. It should then display from that letter to the end of the message.
  3. Once you have written it in pseudocode create it in Python, save it with a sensible name and test it out.

Learn It: Concatenation

Concatenation

  • Concatenation means joining two strings together and this is done using the + symbol in both pseudocode and Python.

Strings_Concatenation.png

  • Please note, the “ “ has been added in the middle to join the names with a space between them.

Strings_Concatenation_Table.png

Badge It: Pseudocode Challenge

Silver - Data Type Conversions

  1. Write pseudocode to assign a 7-digit number to an integer variable.
  2. Convert this to a string, and output the middle three digits.

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Learn It: ASCII Character codes

ASCII Character codes

  • ASCII stands for “American Standard Code for Information Interchange”. Using this code, every character can be represented as a 7-bit binary pattern, allowing 128 different characters to be represented.
  • The table below shows how each upper and lower-case letter is represented along with numbers and some symbols:

ascii_table_lge.png

  • If you want to convert a character into an ASCII code, you can convert that character to the corresponding ASCII code as shown below:

Strings_ASCII.png

  • If you want to convert an ASCII code into a character, you can convert this as shown below:

Strings_CharTo_ASCII.png

Learn It: String Conversions

String Conversions

  • Sometimes we need to change the data type of a variable from a string to an integer or a real (float) number or vice versa.

Strings_Conversions.png

  • Python is quite simple and does not really care about the current data type, it only needs to know what you are converting it to (int, float or str).
  • Whereas the pseudocode is much more specific and needs you to know the current data type and the required data type you are converting it to.

Badge It: Concatenation Challenge

Gold - Concatenation

  1. Create a Python program which will ask the user to enter their date of birth in the format dd/mm/yyyy.
  2. It should also ask them to enter their first name and then enter their surname.
  3. The program should take the digits for the date of birth and add them together (for instance if the date was 13/02/2002 it should add together 1 + 3 + 0 + 2 + 2 + 0 + 0 + 2 = 10).
  4. It should join the first 3 digits of their surname to the last letter of their first name and join this to the number that was created. So, if their name is Jemima Puddle-Duck and their date of birth was the 13/02/2002 the program should display Puda10.
  5. Make sure you save the program with a sensible name and test it out.

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Badge It: ASCII Challenge

Platinum - ASCII Challenge

  1. Write pseudocode statements to accept an uppercase character from the user, and output the next character in the alphabet.
  2. If the user inputs Z, the letter A should be outputted.
  3. Now create a Python program for this task.

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