15-112 Fundamentals of Programming

 
def getPositiveInteger():
    userInput = 0       
    while(userInput <= 0):     
        userInput = int(input("Enter a positive integer: "))
    return userInput

 
# Repeating a block of code a certain number of times with a while loop:
i = 0
numRepetitions = 10       
while (i < numRepetitions):         
    # Some block of code
    # ...
    counter += 1     

 
def countToN(n):
    counter = 1       
    while(counter <= n):
        print(counter)
        counter += 1

countToN(7)     

 
def sumToN(n):
    counter = 1
    total = 0       
    while(counter <= n):
        total += counter
        counter += 1
    return total

print(sumToN(5))  # prints 15

def sumFromMToN(m, n):
    counter = m
    total = 0       
    while(counter <= n):
        total += counter
        counter += 1
    return total

print(sumFromMToN(3,6))  # prints 18    

 
def leftmostDigit(n):
    
    while (n >= 10):
        
        n = n // 10    
    return n

print(leftmostDigit(1234))  # prints 1
print(leftmostDigit(-1234))  # prints -1234 (wrong answer)

def leftmostDigit(n):

    n = abs(n)    
    while (n >= 10):
        
        n = n // 10    
    return n

print(leftmostDigit(-1234))  # prints 1    

 
def nthAwesome(n):
    found = 0
    guess = 0
    while (found <= n):
        if (isAwesome(guess)): 
            found += 1
        guess += 1
    return guess - 1

def isAwesome(m):
    return ((m % 3) == 0) or ((m % 5) == 0)   

 
for i in [1, 2, 3, 4]:
    print(i)

# the following does the same thing
# think of range(m, n) as the list [m, m+1, .., n-1]
for i in range(1, 5):
    print(i)

# range(n) is the same as range(0, n)
# note that it starts from 0!
for i in range(5):
    print(i)

 
# this prints the letters of "Hello", each one on a separate line
for c in "Hello":
    print(c)

 
# If you know how many iterations are needed,
# use a for loop rather than a while loop.
def sumToN(n):
    total = 0
    for i in range(n+1):
        total += i
    return total

def sumFromMToN(m, n):
    total = 0
    for i in range(m, n+1):
        total += i
    return total

# think of range(m, n, k) as the list [m, m+k, m+2k, m+3k, ...] 
# (stops before reaching n)
def sumEveryKthFromMToN(m, n, k):
    total = 0
    for i in range(m, n+1, k):
        total += i
    return total

 
def sumOfOddsFromMToN(m, n):
    total = 0
    for x in range(m, n+1):
        if (x % 2 == 1):
            total += x
    return total

def sumOfOddsFromMToN(m, n):
    if (m % 2 == 0):
        # m is even, add 1 to start on an odd
        m += 1
    total = 0
    for i in range(m, n+1, 2):
        total += i
    return total

# This works, but is not clear code!
def sumOfOddsFromMToN(m, n):
    if (n % 2 == 0): n -= 1
    total = 0
    for x in range(n, m-1, -2):
        total += x
    return total

 
def isPrime(n):
    if (n < 2): return False
    for x in range(2, n):
        if(n % x == 0): return False
    return True

 
def fasterIsPrime(n):
    if (n < 2): return False
    maxFactor = round(n**0.5)
    for x in range(2, maxFactor + 1):
        if(n % x == 0): return False
    return True

 
def nthPrime(n):
    found = 0
    guess = 0
    while (found <= n):
        guess += 1
        if (isPrime(guess)):
            found += 1
    return guess