#!/usr/bin/env python
# coding: utf-8

# # Introduction to programming for Geoscientists (through Python)

# # Lecture 2: Solutions to exercises
# ## Gerard J. Gorman (g.gorman@imperial.ac.uk) http://www.imperial.ac.uk/people/g.gorman

# ## <span style="color:blue">Exercise 2.1: Values of boolean expressions</span>

# In[1]:


C = 41

# The value of C must be equal to 40 for this condition to be True. Otherwise,
# this condition is False. Of course, 41 is not equal to 40, so this particular
# condition is False.
C == 40

# Both conditions (C != 40 *and* C < 41) must be True for the whole statement
# to be True. Although the first condition is True, the second condition is
# False since C is not less than 41, so the whole statement is False.
C != 40 and C < 41

# Here, only one of the two conditions needs to be True in order for the whole
# statement to be True. Since C != 40 is True, this particular statement is True.
C != 40 or C < 41

# The *not* keyword just negates whatever condition follows it. In this case,
# C == 40 is False, so 'not C == 40' will return the opposite (True).
not C == 40

# C > 40 is True, so 'not C > 40' is False
not C > 40

# For this condition to be True, C must either be less than 40 *or* equal to 40.
# If neither of these are True, then the condition is False.
C <= 41

# The *not* keyword will negate the result, so 'not False' is 'True'.
not False

# With the *and* logical operator, both conditions must be True for the whole 
# statement to be True. In this particular case, the statement is False.
True and False

# With the *or* logical operator, this whole statement is True since at least
# one of the conditions is True.
False or True

# None of the conditions are True, so the whole statement is False.
False or False or False

# At least one of the conditions is False, so the whole statement is False.
True and True and False

# The integer value of False is 0, so this statement is True
False == 0

# The integer value of True is 1, so this statement is False
True == 0

# This statement is True (see above).
True == 1


# ## <span style="color:blue">Exercise 2.2: Make a Fahrenheit-Celsius conversion table</span>
# Write a program that prints out a table with Fahrenheit degrees 0, 10, 20, ..., 100 in the first column and the corresponding Celsius degrees in the second column.

# In[2]:


# Make a Fahrenheit-Celsius conversion table
F = 0                        # Initialise F
dF = 10                      # Increment for F within the loop
while F <= 100:              # Loop heading with condition
    C = (F - 32)*(5.0/9.0)   # 1st statement inside loop
    print(F, C)              # 2nd statement inside loop
    F = F + dF               # Increment F for the next iteration of the loop.


# ## <span style="color:blue">Exercise 2.3: Write an approximate Fahrenheit-Celsius conversion table</span>
# Many people use an approximate formula for quickly converting Fahrenheit ($F$) to Celsius ($C$) degrees:</br></br>
# $C \approx \hat{C} = \frac{F − 30}{2}$</br></br>
# Modify the program from the previous exercise so that it prints three columns: $F$, $C$, and the approximate value $\hat{C}$.

# In[3]:


# Write an approximate Fahrenheit-Celsius conversion table
F = 0                      # Initialise F
dF = 10                    # Increment for F within the loop
while F <= 100:            # Loop heading with condition
    C = (F - 32)*(5.0/9.0) # 1st statement inside loop
    C_hat = (F - 30)/2.0   # Compute the approximate value of C.
    print(F, C, C_hat)      # 2nd statement inside loop
    F = F + dF             # Increment F for the next iteration of the loop.


# ## <span style="color:blue">Exercise 2.4: Store odd numbers in a list</span>
# Modify the program from the previous exercise to store the generated odd numbers in a list. Start with an empty list and use a while loop where you in each pass of the loop append a new element to the list. Finally, print the list elements to the screen.

# In[4]:


# Store odd numbers in a list
n = 16

i = 1
odd_numbers = []
while i <= n:
    odd_numbers.append(i) # Append the odd number 'i' to the list called 'odd_numbers'
    i = i + 2
print("The odd numbers list = ", odd_numbers)


# ## <span style="color:blue">Exercise 2.5: Repeat the previous exercise using: a for loop, list comprehension and the range function</span>

# In[5]:


# Generate odd numbers by a list comprehension
n = 16

# Use list comprehension to generate the list of odd numbers.
# Remember to choose the step size to be 2 here.
odd_numbers = [i for i in range(1, n+1, 2)]
print("The odd numbers list = ", odd_numbers)

# You could also do (using the default 'start' and 'step' values in the range function)
odd_numbers = [2*i + 1 for i in range(int((n + 1)/2))]
print("The odd numbers list = ", odd_numbers)