Add loops and update lecture2.md

Author: Sahil

day2/functions.py

@@ -0,0 +1,51 @@
+# print numbers from 1 to 10 to the screen
+'''
+print(1)
+print(2)
+...
+print(10)
+
+The above is not a good practice since our requirement
+might change and we might have to print from 1 to n, where n is the input.
+Also, the code is repititive, that is why language provides loop constructs!
+'''
+
+# for loops in python do not have initialization, condition, update statement like in other langs
+# in keyword is used along with for, to iterate over items in a container or sequence
+
+for n in range(10):
+  print(n, end=' ')
+print() # by default, end = '\n'
+
+# the above code prints '0 1 2 ... 9'
+# we want to print '1 2 3 ... 10'
+
+for n in range(1, 11):
+  print(n, end=' ')
+print()
+
+# let us say we want to print all even numbers from 1 to 10
+
+for n in range(2, 11, 2):
+  print(n, end=' ')
+print()
+
+# can use list operator before range, to print the items in the range
+print(list(range(2, 11, 2)))
+
+# doing the same thing using a while loop
+counter = 0
+while (counter < 10):
+  counter += 1
+  print(counter, end=' ')
+print()
+
+# NOTE: while loops usually have a statement to update the sentinel value (being checked in condition)
+# otherwise the loop can run infinitely, use Ctrl-C to exit the infinite loop
+# the loop below runs infinitely
+
+'''
+  counter = 0
+  while (counter < 10):
+    print(counter, end=' ')
+'''

day2/jump_statements.py

@@ -0,0 +1,8 @@
+vegetable_market = ["onion", "tomato", "broccoli", "cabbage"]
+
+if "carret" in vegetable_market:
+  print("Bought carret!")
+elif "cabbage" in vegetable_market:
+  print("Bought cabbage!")
+else:
+  print("Came back empty handed...")

day2/loops.py

@@ -0,0 +1,15 @@
+'''
+Program to print multiplication tables of numbers from 1 to n
+'''
+n = int(input())
+
+for multiple in range(1, 11):
+  for number in range(1, n + 1):
+    print(number*multiple, end=' ')
+  print()
+
+# formatted output
+for multiple in range(1, 11):
+  for number in range(1, n + 1):
+    print("%4d"%(number*multiple), end=' ')
+  print()

day2/market.py

@@ -16,4 +16,48 @@
 print(res_two) # True
 
 user_logged_in = True
-print(not user_logged_in)
+print(not user_logged_in)
+
+# the integer 0 is always False, and every other number, is True
+x = bool(0)
+y = bool(-1)
+z = bool(1)
+print(x, y, z) # False True True
+
+# strings are compared lexicographically, i.e. by ASCII value of the characters
+# you can remeber that capital letters come before lower case ones
+print("Scaler" > "Interviewbit") # True as 'S' comes after 'I'
+print('s' > 'S') # True
+print("Scaler" == "Interviewbit") # False
+
+# Identity comparisons, is keyword is used
+# if the compared objects are stored in the same memory location, returns true
+a = "Scaler"
+b = "Scaler"
+print(a is b)
+print(id(a))
+print(id(b))
+
+# bitwise operators
+a = 3
+b = 5
+c = a & b
+'''
+Bitwise AND (&)
+In result, bit is set at those positions where it is set in both the operands
+  011
+& 101
+  ---
+  001
+  ---
+'''
+print(c)
+
+# Exercise
+a = False
+b = True
+c = True
+
+print (a or b and c)
+
+# Read about operator precedences

day2/multiplication_tables.py

@@ -0,0 +1,40 @@
+'''
+Program to find sum of digits of a number
+'''
+n = int(input())
+
+# say n = 1234, how do you compute the sum of the digits?
+# you see all the digits, 1, 2, 3, 4, and add them up in a go, boom => 10 is the answer
+
+# How do we program the computer to do this for us?
+# We should follow the same technique, right?
+# Loop through all the digits, and add them up one by one!
+# So, our computer will store the result at some place, we need to create a variable
+# Say sum = 0
+# How to find a particular digit?
+# n = 1234, can we say last digit is the one we get after finding remainder when n is divided by 10
+# i.e. n % 10 = 4, add this 4 to the sum, now sum = 4
+# Now, we can divide n by 10, to get n' = 1234//10 = 123 (integer division!)
+# We continue this process, until n becomes zero!!!
+# Pseudocode:
+'''
+  n = input from user
+  sum = 0
+  while (n > 0)
+    d = last digit of n (i.e. n % 10)
+    add d to sum
+    divide n by 10
+  print(sum)
+'''
+
+sum = 0
+while (n > 0):
+  d = n % 10
+  sum += d # shorthand for sum = sum + d
+  n //= 10 # shorthand for n = n//10
+print(sum)
+
+# Try yourself:
+# 1. Count digits in a number
+# 2. Reverse a number
+# 3. Find all factors of a number