For loop exercises

import numpy as np

You may remember you can print a number (or anything else) with the print function, like this:

print(5)

5

Use a for loop to print out all the numbers from 3 through 7, one number on each line.

# Your code here.

Make an empty array called my_array. Use a for loop to append all the numbers between 0 and 10 (inclusive) to my_array. Show the array at the end of the loop.

# Your code here.
my_array = np.array([])

Make a new variable total equal to 0. Use a for loop to add all the numbers from 15 through 32 to total. Print the value at the end of the loop.

Hint - here is a statement where I add 10 to the variable my_variable: my_variable = my_variable + 10.

# Your code here.
total = 0

Use a for loop to add up all the even numbers from -102 through 98. Hint: you may like to use the step argument.

# Sum of all even numbers from -102 through 98.
total = 0

Have a look at the definition of the factorial.

For example, the factorial of 5, written \(5!\) is 1 * 2 * 3 * 4 * 5.

Use a for loop to calculate \(15!\). Print out the result.

Note: those of you on Windows will have to start with a floating point value - as in factorial = 1.0 - in order to avoid a nasty interaction between Numpy, Windows, and integers.

# Calculate 15!
# Note the floating point number to start.
factorial = 1.0

These are getting a bit harder.

You can break out of a for loop using the break statement. Here I break out of the for loop, when I get to 6. Notice I never get to 7 or any number higher than 6. The break statement says, “stop the for loop now, and go directly to the first statement after the for loop”.

for i in np.arange(1000):
    print(i)
    if i == 6:
        print("Stopping here, where i == 6")
        break
print("I have finished the for loop now.")

0
1
2
3
4
5
6
Stopping here, where i == 6
I have finished the for loop now.

Make sure you understand what is going on in the cell above. When you do, try using this technique to find the largest integer \(n\) where \(n! < 10^6\). Print out \(n\) and \(n!\). Hint for your for loop: \(n\) is less than 100.

factorial = 1
last_factorial = 1
threshold = 1000000
# Your code here

Here is an array of 50 numbers:

# Run this cell to define the "values" array
values = np.array([ 3,  32,  39, -3,  34,  28,   9,  36,
         -4,  20,  -4,  13,  32,  9,  14, 999,   2,  20,  18,
         12,  13,  25,  25,   2,  17,  39, 39,   4,  26,   7,
          1,  36,  31,  15,  25,  19, 999, -4,  -3,  24,   7,
         14,  -2,  35,  18,  23,  34,  14, 11,  25])

Add up all the numbers in this array, until you get to the first value of 999. Print the sum of all the values up to, but not including, the first 999. For example, if the array was np.array([2, 6, 4, 999, 11]), then the result would be: 2 + 6 + 4 == 12. What is the equivalent result for the values array above?

# Your code here.

The next cell is a slight variation. Add all the numbers in this array, up to, but not including, the first value of 999. This time, discard any negative values you find. For example, if the array was np.array([1, 7, -3, 4, 999, 13]), then the result would be: 1 + 7 + 4 == 12. What is the equivalent result for the values array above?

# Your code here.