Python While Loops
We are going to be looking at the While loop in python.
The while loop in python is a control flow statement that repeatedly executes a block of code as long as a specified condition is true.
Â
Example 1 Basic While Loop
Here, we are using the while loop to print numberd from 1 to 9.
It keeps increasing x by 1 until it reaches 10.
x = 1 while x < 10: print(x) x = x + 1 
Example 2 Basic While Loop
This loop prints the current number (x) and running sum in each iteration.
It adds the next x to sum after printing, repeating until x is 10.
x = 1 sum = 0 while x < 10: print('number: ' + str(x) + ', sum: ' + str(sum)) x = x + 1 sum +=x 
Example 1 - if else state location
This line of code creates an infinite loop because i starts at 2 and keeps increasing, so the condition i > 1 is always true.
i = 2 while i > 1: print('infinite') i = i + 1 
Example 4 break and Continue
This while loop prints numbers from 1 to 4. When x reaches 5, the break statement exits the loop early.
x = 1 while x < 10: if x == 5: break print(x) x = x + 1 
This loop prints numbers from 1 to 9, but skips 5. when x is 5, “continue” skips the print() and goes to the next iteration
x = 1 while x < 10: if x == 5: x = x + 1 continue print(x) x = x + 1 
Example 5 While Loops with inputs
Here, we keep asking the user for a number, square it, and print the result. It stop when the user enters ‘z’. Inputs are cast to integers before squaring.
while True: x = input("Enter Number ") if x == 'z': break print (int(x) * int(x)) #need to cast as int 
Example 5b variant While Loops with inputs
Here, we ask the user for a positive number less than 20. If the input is invalid, it keeps prompting until valid.
Then it prints the square of the number.
x = input("Enter positive Number less than 20 ") while int(x) < 0 or int(x) > 20: print("Wrong Number") x = input("Enter positive Number less than 20 ") print (int(x) * int(x)) #need to cast as int 
Example 6 lists
Here we loop through the list and add each positive number to sum, stopping if it reaches the end or encounters a non-positive number.
It prints the runnung total after each addition.
list = [1, 3, 7, 11, 6, 8, 10] sum = 0 x = 0 while x < len(list) and list[x] > 0: sum += list[x] x +=1 print(sum) 
Example 6b lists
This code iterates through the list, and for each element at a positive index, it adds the value to even_sum if thr index is even, or to odd_sum if the index is odd.
list = [1, 3, 7, 11, 6, 8, 10] even_sum = 0 odd_sum = 0 x = 0 while x < len(list) and list[x] > 0: if x % 2 == 0: even_sum += list[x] else: odd_sum += list[x] x +=1 
even_sum 
odd_sum 
Example 7 multiple
Here we use a nested loop to print a multiplication table for numbers 2 through 8, each multiplied by 1 through 3.
# Initialize variables x = 2 # Outer while loop while x <= 8: y = 1 # Inner while loop while y <= 3: # Perform calculation using both x and y result = x * y # Print the result print(f"{x} * {y} = {result}") # Increment y y += 1 # Increment x x += 1 
