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   "source": [
    "# Introduction to programming for Geoscientists (through Python)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Lecture 2: Solutions to exercises\n",
    "## Gerard J. Gorman (g.gorman@imperial.ac.uk) http://www.imperial.ac.uk/people/g.gorman"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <span style=\"color:blue\">Exercise 2.1: Values of boolean expressions</span>"
   ]
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    "C = 41\n",
    "\n",
    "# The value of C must be equal to 40 for this condition to be True. Otherwise,\n",
    "# this condition is False. Of course, 41 is not equal to 40, so this particular\n",
    "# condition is False.\n",
    "C == 40\n",
    "\n",
    "# Both conditions (C != 40 *and* C < 41) must be True for the whole statement\n",
    "# to be True. Although the first condition is True, the second condition is\n",
    "# False since C is not less than 41, so the whole statement is False.\n",
    "C != 40 and C < 41\n",
    "\n",
    "# Here, only one of the two conditions needs to be True in order for the whole\n",
    "# statement to be True. Since C != 40 is True, this particular statement is True.\n",
    "C != 40 or C < 41\n",
    "\n",
    "# The *not* keyword just negates whatever condition follows it. In this case,\n",
    "# C == 40 is False, so 'not C == 40' will return the opposite (True).\n",
    "not C == 40\n",
    "\n",
    "# C > 40 is True, so 'not C > 40' is False\n",
    "not C > 40\n",
    "\n",
    "# For this condition to be True, C must either be less than 40 *or* equal to 40.\n",
    "# If neither of these are True, then the condition is False.\n",
    "C <= 41\n",
    "\n",
    "# The *not* keyword will negate the result, so 'not False' is 'True'.\n",
    "not False\n",
    "\n",
    "# With the *and* logical operator, both conditions must be True for the whole \n",
    "# statement to be True. In this particular case, the statement is False.\n",
    "True and False\n",
    "\n",
    "# With the *or* logical operator, this whole statement is True since at least\n",
    "# one of the conditions is True.\n",
    "False or True\n",
    "\n",
    "# None of the conditions are True, so the whole statement is False.\n",
    "False or False or False\n",
    "\n",
    "# At least one of the conditions is False, so the whole statement is False.\n",
    "True and True and False\n",
    "\n",
    "# The integer value of False is 0, so this statement is True\n",
    "False == 0\n",
    "\n",
    "# The integer value of True is 1, so this statement is False\n",
    "True == 0\n",
    "\n",
    "# This statement is True (see above).\n",
    "True == 1"
   ]
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   "source": [
    "## <span style=\"color:blue\">Exercise 2.2: Make a Fahrenheit-Celsius conversion table</span>\n",
    "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."
   ]
  },
  {
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   "execution_count": 2,
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 -17.77777777777778\n",
      "10 -12.222222222222223\n",
      "20 -6.666666666666667\n",
      "30 -1.1111111111111112\n",
      "40 4.444444444444445\n",
      "50 10.0\n",
      "60 15.555555555555557\n",
      "70 21.11111111111111\n",
      "80 26.666666666666668\n",
      "90 32.22222222222222\n",
      "100 37.77777777777778\n"
     ]
    }
   ],
   "source": [
    "# Make a Fahrenheit-Celsius conversion table\n",
    "F = 0                        # Initialise F\n",
    "dF = 10                      # Increment for F within the loop\n",
    "while F <= 100:              # Loop heading with condition\n",
    "    C = (F - 32)*(5.0/9.0)   # 1st statement inside loop\n",
    "    print(F, C)              # 2nd statement inside loop\n",
    "    F = F + dF               # Increment F for the next iteration of the loop."
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <span style=\"color:blue\">Exercise 2.3: Write an approximate Fahrenheit-Celsius conversion table</span>\n",
    "Many people use an approximate formula for quickly converting Fahrenheit ($F$) to Celsius ($C$) degrees:</br></br>\n",
    "$C \\approx \\hat{C} = \\frac{F − 30}{2}$</br></br>\n",
    "Modify the program from the previous exercise so that it prints three columns: $F$, $C$, and the approximate value $\\hat{C}$."
   ]
  },
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   "execution_count": 3,
   "metadata": {},
   "outputs": [
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     "name": "stdout",
     "output_type": "stream",
     "text": [
      "0 -17.77777777777778 -15.0\n",
      "10 -12.222222222222223 -10.0\n",
      "20 -6.666666666666667 -5.0\n",
      "30 -1.1111111111111112 0.0\n",
      "40 4.444444444444445 5.0\n",
      "50 10.0 10.0\n",
      "60 15.555555555555557 15.0\n",
      "70 21.11111111111111 20.0\n",
      "80 26.666666666666668 25.0\n",
      "90 32.22222222222222 30.0\n",
      "100 37.77777777777778 35.0\n"
     ]
    }
   ],
   "source": [
    "# Write an approximate Fahrenheit-Celsius conversion table\n",
    "F = 0                      # Initialise F\n",
    "dF = 10                    # Increment for F within the loop\n",
    "while F <= 100:            # Loop heading with condition\n",
    "    C = (F - 32)*(5.0/9.0) # 1st statement inside loop\n",
    "    C_hat = (F - 30)/2.0   # Compute the approximate value of C.\n",
    "    print(F, C, C_hat)      # 2nd statement inside loop\n",
    "    F = F + dF             # Increment F for the next iteration of the loop."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <span style=\"color:blue\">Exercise 2.4: Store odd numbers in a list</span>\n",
    "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."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The odd numbers list =  [1, 3, 5, 7, 9, 11, 13, 15]\n"
     ]
    }
   ],
   "source": [
    "# Store odd numbers in a list\n",
    "n = 16\n",
    "\n",
    "i = 1\n",
    "odd_numbers = []\n",
    "while i <= n:\n",
    "    odd_numbers.append(i) # Append the odd number 'i' to the list called 'odd_numbers'\n",
    "    i = i + 2\n",
    "print(\"The odd numbers list = \", odd_numbers)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## <span style=\"color:blue\">Exercise 2.5: Repeat the previous exercise using: a for loop, list comprehension and the range function</span>"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "The odd numbers list =  [1, 3, 5, 7, 9, 11, 13, 15]\n",
      "The odd numbers list =  [1, 3, 5, 7, 9, 11, 13, 15]\n"
     ]
    }
   ],
   "source": [
    "# Generate odd numbers by a list comprehension\n",
    "n = 16\n",
    "\n",
    "# Use list comprehension to generate the list of odd numbers.\n",
    "# Remember to choose the step size to be 2 here.\n",
    "odd_numbers = [i for i in range(1, n+1, 2)]\n",
    "print(\"The odd numbers list = \", odd_numbers)\n",
    "\n",
    "# You could also do (using the default 'start' and 'step' values in the range function)\n",
    "odd_numbers = [2*i + 1 for i in range(int((n + 1)/2))]\n",
    "print(\"The odd numbers list = \", odd_numbers)"
   ]
  }
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