CMU 15-110: Principles of Computing
Loops

1. for loops
   • using range(n)
   • using range(lo, hi)
   • using range(lo, hi, step)
2. while loops
3. Infinite loops

1. for loops
   • using range(n)
     # print the integers from 0 to 9 (not 10) for x in range(10): print(x)
     
     Example: sumToN
     def sumToN(n): result = 0 for x in range(n+1): result += x return result print('n sumToN(n)') for n in range(10): print(n, ' ', sumToN(n))
   
   
   • using range(lo, hi)
     # print the integers from 20 to 29 for x in range(20, 30): print(x)
     
     Example: factorial
     def factorial(n): result = 1 for x in range(2, n+1): result *= x return result print('n factorial(n)') for n in range(10): print(n, ' ', factorial(n))
   
   
   • using range(lo, hi, step)
     # print the integers from 20 to 49 by 5's for x in range(20, 50, 5): print(x)
     
     Example: sumOfOddsToN
     def sumOfOddsToN(n): result = 0 for x in range(1, n+1, 2): result += x return result print('n sumOfOddsToN(n)') for n in range(10): print(n, ' ', sumOfOddsToN(n))


2. while loops
   • leftmostDigit
     def leftmostDigit(n): n = abs(n) while (n >= 10): n = n//10 return n print(leftmostDigit(72658489290098)) # 7
   
   
   • digitSum
     def digitSum(n): result = 0 n = abs(n) while (n > 0): onesDigit = n%10 n = n//10 result += onesDigit return result print(digitSum(201401)) # 2+0+1+4+0+1 == 8


3. Infinite loops
   def addSomeNumbers(): total = 0 while True: rawInput = input('Enter a number (or just hit enter to quit) --> ') if (rawInput == ''): return total total += int(rawInput) total = addSomeNumbers() print('Total:', total)