# 
# function_examples.py
# 
# Example functions from lecture
#
# Computer Science 111
#

def triple(x):
    """ Returns the triple of the input x. """
    return 3*x

def undo(s):
    """ Adds the prefix 'un' to the input s. """
    return 'un' + s

def redo(s):
    """ Adds the prefix 're' to the input s. """
    return 're' + s

def circle_area(diam):
    """ Computes the area of a circle
        with a diameter diam.
    """
    radius = diam / 2
    area = 3.14159 * (radius**2)
    return area

def rect_perim(l, w):
    """ Computes the perimeter of a rectangle
        with length l and width w.
    """
    return 2*l + 2*w

def avg_first_last(values):
    """ Takes a list of numbers with at least one element and returns the 
        average of the first and last elements.
    """
    first = values[0]
    last = values[-1]
    return (first + last) / 2

def abs_value(x):
    """ Returns the absolute value of the iput x """
    if x < 0:
        x = -1 * x
    return x

def pass_fail(avg):
    """ Takes a numeric average avg and returns a string that indicates 
        if the average is passing or failing.
    """
    if avg >= 60:
        grade = 'pass'
    else:
        grade = 'fail'
    return grade

def letter_grade(avg):
    """ Takes a numeric average avg and returns a string that indicates 
        the letter grade corresponding to that average.
    """
    if avg >= 90:
        grade = 'A'
    elif avg >= 80:
        grade = 'B'
    elif avg >= 70:
        grade = 'C'
    elif avg >= 60:
        grade = 'D'
    else:
        grade = 'F'
    return grade