# Python Course 3: Data Types and Integers

## Good Practice

Which of the following is better programming practice? Why?

``````x = 35.51*1.17
print(x)``````

or

``````pounds = 35.51
euroRate = 1.17
euros = pounds * euroRate

print("£", pounds ,  " = " , euros , " euros")
print("at a rate of " , euroRate , " euros to the pound")``````

## Formatting

Take a look at the output from the second piece of code

``````£ 35.51  =  41.546699999999994  euros
at a rate of  1.17  euros to the pound``````

This would be better if it read 41.55 euros, rather than 41.546699999999994

Also, take a look at this line

``print("£", pounds ,  " = " , euros , " euros")``

All those commas and speech marks are confusing. It’s easy to make a mistake when entering them.

There’s a better way to format your data.

``````pounds = 35.51
euroRate = 1.17
euros = pounds * euroRate

print("£ {} = {} euros".format(pounds, euros))
print("at an rate of {} euros to the pound".format(euroRate))``````

The above does the same as the original code. It has the advantage of being slightly easier to enter and read. As an added bonus, you can format the number of decimal places

``````pounds = 35.51
euroRate = 1.17
euros = pounds * euroRate

print("£ {} = {:.2f} euros".format(pounds, euros))
print("at an rate of {} euros to the pound".format(euroRate))``````

Notice the {:.2f}. This says “format the number as a float (a decimal) to 2 decimal places”

This produces the following output

``````£ 35.51 = 41.55 euros
at a rate of 1.17 euros to the pound
``````

Much more user friendly!

## Loop Question

Use a while loop to produce the sequence 0.1, 0.2, 0.3, …1.0

``````number = 0.1
while number <=1:
print(number)
number = number + 0.1``````

Produces

``````0.1
0.2
0.30000000000000004
0.4
0.5
0.6
0.7
0.7999999999999999
0.8999999999999999
0.9999999999999999``````

Format the number for a neater answer

``````number = 0.1
while number <=1:
print("{:.1f}".format(number))
number = number + 0.1

0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0``````

## Number bases

You can format numbers into different bases as follows

``````print("{:d}".format(17))
print("{:b}".format(17))
print("{:X}".format(17))
``````

The numbers are printed in denary, binary and hexadecimal.

``````17
10001
11``````

Remember that the input command reads strings. You have to convert strings to integers (whole numbers) or floats (decimals) if you want to use them to perform calculations.

## Examples

1) Write a program that prompts the user to enter the length and width of a rectangle. Output the area of the rectangle

``````length = int(input("Enter the length of the rectangle"))
width = int(input("Enter the width of the rectangle"))
area = length*width
print("The rectangle has an area of {}".format(area))``````

2) To convert miles to kilometers, you multiply the number of miles by 1.609. Write a program that prompts the user to enter the number of miles, and then output the answer converted to kilometers

Note the use of float as a user may input 12.5 miles, for example.

``````miles = float(input("Enter the number of miles"))
kilometers = miles * 1.609
print("{} miles = {:.2f} kilometers".format(miles,kilometers))``````

## Exercise

1. Write a program with two variables, length and width, that outputs the perimeter of a rectangle. Test it with length = 5 and width = 4.
2. At the time of writing, the exchange rate for pounds to euros is 1 GBP = 1.19984 Euros. Write a program that will convert pounds to euros. Test it using the data GBP4.50 (Don’t forget to convert the input to a float!)
3. Now write a program to convert euros to pounds. Test it using the data Euro 7.40
4. Prompt the user to input a number. Output the square of that number.
5. Prompt the user to input two numbers. Output the average of those two numbers.
6. Prompt the user to input three numbers. Output the sum and the average of those three numbers.
7. Assume pi = 3.1415. Prompt the user to input the radius of a circle. Output the circumference and the diameter of that circle

## Extension: Fahrenheit to Celsius

Here are the formulas to convert from Fahrenheit to Celsius and back again.

°F to °C Deduct 32, then multiply by 5, then divide by 9 °C to °F Multiply by 9, then divide by 5, then add 32

1. Now write a program to convert Celsius to Fahrenheit. Use the test data to check your program.
2. Write a program to convert Fahrenheit to Celsius. Again, use the test data below to check your program.

### Test data

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