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Lesson-03

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03-simple-calculator-with-input

Create Simple Calculator With Input

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Lesson-03

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python-course

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03-simple-calculator-with-input

Create Simple Calculator With Input

Description here...

Lesson-03

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python-course

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03-simple-calculator-with-input

Create Simple Calculator With Input

Description here...

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Lesson Objectives

Lesson Objectives

Lesson Objectives

- Get user input with input() function.
- Check types withy type() function.
- Convert Types in python
- Create a simple calculator

Lesson Summary

Lesson Summary

Lesson Summary

Simple Exercise: Calculator

Let's practice and create a simple calculator.

The goal is to ask user to provide us numbers and then we'll join them and report the results in the console. I know it sounds too simple, but there is a tricky part that makes it a great excercise.

So let's dive in.

How To Get User Input?

To ask user for an input we can use built-in function called input().

Since it's a function we need to use its name and then place parenthesis () for any arguments. Sometimes functions don't need any arguments, or can even have multiple of them. In case of input() we need to provide a string message that user will see in the console.

Also, keep in mind that user input will be returned as string. This will be an important point in a moment. So let's try to get 2 numbers and add them together.

Like this:

num_a = input("Enter First Number: ")
num_b = input("Enter Second Number: ")

total = num_a + num_b
print(total)
num_a = input("Enter First Number: ")
num_b = input("Enter Second Number: ")

total = num_a + num_b
print(total)
num_a = input("Enter First Number: ")
num_b = input("Enter Second Number: ")

total = num_a + num_b
print(total)

Now if you run this code you will notice that you need to provide input in the console. I will provide 2 and 3. And then we can see we printed the total value as 23.

Hold on a second, 2+3 is not equal 23. What's going on?

Remember I mentioned that input() returns string? So we aren't making an arithmetic math here... We're just adding 2 strings together. Similar to ab + cd = 'abcd'

So if we want to do math, we need to convert our strings to numbers first. That's why it's important to know types of your variables in python. And if you're unsure, you can always double check with another built-in function called type()

How To type() ?

The type() function takes any object in your code as an argument, and it returns the class of that object.

It's great to use during development if you get confused. It can also be used for logical statements to avoid issues, but more on that later in another lesson.

For now, here's simple example how to print the type of your variables:

# 📦Random Values
num_a = "10"
num_b = 20
list_nums = ["10", 20]

# 🔎Check Types
print(type(num_a))
print(type(num_b))
print(type(list_nums))
# 📦Random Values
num_a = "10"
num_b = 20
list_nums = ["10", 20]

# 🔎Check Types
print(type(num_a))
print(type(num_b))
print(type(list_nums))
# 📦Random Values
num_a = "10"
num_b = 20
list_nums = ["10", 20]

# 🔎Check Types
print(type(num_a))
print(type(num_b))
print(type(list_nums))

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Convert Types in Python

So, we know that we get strings from the input() function. But we need to convert it into integer or float to do some math.

To convert or create types in Python we need to use special built-in functions for each type. They either create default value, or convert the value you provide from other types, if it's logically possible.

The functions:

  • str() – Create an empty string "" or convert a value into a string

  • int() – Create 0 or convert a value into an integer

  • float() – Create 0.0 or convert a value into a floating-point number

  • bool() – Create False or convert a value into True/False

  • list() – Create [] or convert an iterable into a list

  • tuple() – Create () or convert an iterable into a tuple

  • set() – Create empty set or convert an iterable into a set (unique elements)

  • dict() – Create empty dict or convert a mapping/sequence of pairs into a dictionary


In our case, we want to convert strings into integers, so we need to use int() function. Here's how it works:

# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = int(str_num_a)
num_b = int(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)
# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = int(str_num_a)
num_b = int(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)
# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = int(str_num_a)
num_b = int(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)

This time if you run your code and provide 2 and 3 you will get 5 as total.
So this time we are actually doing math!

Floating numbers

But what if we decide to add floating numbers like 2.5 + 2.5 ?

Alright, so we can't convert "2.5" into an integer… But what about converting into a float number? (float is a number with decimal point e.g. 3.14 )

# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = float(str_num_a)
num_b = float(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)
# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = float(str_num_a)
num_b = float(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)
# 🙋‍♂️Get User Input
str_num_a = input("Enter First Number: ")
str_num_b = input("Enter Second Number: ")

# 🔁Convert String to Int
num_a = float(str_num_a)
num_b = float(str_num_b)

# 🧮Calculate Total
total = num_a + num_b
print(total)

This time 2.5 + 2.75 = 5.25 . It works, we're back to real science💥!

Examples

Alright, let's go through multiple examples quickly, so you get an idea of what's going on when you convert your basic data types. I highly recommend you to copy these examples and run codes yourself.

# Numbers
x          = 10
str_x      = str(x)       # Convert integer to string: '10'
float_x    = float(x)     # Convert integer to float: 10.0
bool_x     = bool(x)      # Convert integer to boolean: True (non-zero is True)
bool_neg_x = bool(0)      # Convert 0 to boolean: False
# Numbers
x          = 10
str_x      = str(x)       # Convert integer to string: '10'
float_x    = float(x)     # Convert integer to float: 10.0
bool_x     = bool(x)      # Convert integer to boolean: True (non-zero is True)
bool_neg_x = bool(0)      # Convert 0 to boolean: False
# Numbers
x          = 10
str_x      = str(x)       # Convert integer to string: '10'
float_x    = float(x)     # Convert integer to float: 10.0
bool_x     = bool(x)      # Convert integer to boolean: True (non-zero is True)
bool_neg_x = bool(0)      # Convert 0 to boolean: False
# Strings
s          = "123"
int_s      = int(s)       # Convert string to integer: 123
float_s    = float(s)     # Convert string to float: 123.0
bool_s     = bool(s)      # Convert  string to boolean: True (if not empty)
bool_empty = bool("")     # Convert empty string to boolean: False
# Strings
s          = "123"
int_s      = int(s)       # Convert string to integer: 123
float_s    = float(s)     # Convert string to float: 123.0
bool_s     = bool(s)      # Convert  string to boolean: True (if not empty)
bool_empty = bool("")     # Convert empty string to boolean: False
# Strings
s          = "123"
int_s      = int(s)       # Convert string to integer: 123
float_s    = float(s)     # Convert string to float: 123.0
bool_s     = bool(s)      # Convert  string to boolean: True (if not empty)
bool_empty = bool("")     # Convert empty string to boolean: False
# Booleans
bool_true  = bool(1)       # True
bool_false = bool(0)      # False
bool_list  = bool([])      # Convert empty list to boolean: False
bool_dict  = bool({})      # Convert empty dict to boolean: False
bool_str   = bool("Hello")  # Convert non-empty string to boolean: True
# Booleans
bool_true  = bool(1)       # True
bool_false = bool(0)      # False
bool_list  = bool([])      # Convert empty list to boolean: False
bool_dict  = bool({})      # Convert empty dict to boolean: False
bool_str   = bool("Hello")  # Convert non-empty string to boolean: True
# Booleans
bool_true  = bool(1)       # True
bool_false = bool(0)      # False
bool_list  = bool([])      # Convert empty list to boolean: False
bool_dict  = bool({})      # Convert empty dict to boolean: False
bool_str   = bool("Hello")  # Convert non-empty string to boolean: True

Outro

By now you should have a good understanding of basic data types in python and how to control them. It's very crucial to keep track of what data type is your data, so you can provide correct arguments later on.

And as you've seen with our simple calculator, if you forget to convert strings to numbers, you might have a faulty calculator.

Happy Coding!

🙋‍♂️ See you in the next lesson.
- EF

Happy Coding!

🙋‍♂️ See you in the next lesson.
- EF

Happy Coding!

🙋‍♂️ See you in the next lesson.
- EF

Homework

Homework

Homework

Now it's time to build your own calculator.

Try different operators and make your code a little different to mind. You won't learn by simple copy-pasting... You learn by actually experimenting yourself.

⌨️ Happy Coding!

⌨️ Happy Coding!

⌨️ Happy Coding!

Questions

Questions

Questions

If you have any questions, leave them in the YouTube Comments.

If you have any questions, leave them in the YouTube Comments.

If you have any questions, leave them in the YouTube Comments.

Have a Question?

Have a Question?

Have a Question?

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PS. Python can change your career and how you think about problems.
Be Careful 🙂

PS. Python can change your career and how you think about problems.
Be Careful 🙂

PS. Python can change your career and how you think about problems.
Be Careful 🙂

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