Flow control instructions are if, for, and while.

In the next example, we check whether the number is positive, negative, or zero and display the result:

num = 1

if num > 0:
    print("Positive number")
elif num == 0:
    print("Zero")
else:
    print("Negative number")

The following code block finds the sum of all the numbers stored in a list, using a for loop:

numbers = [6, 6, 3, 8, -3, 2, 5, 44, 12]
sum = 0
for val in numbers:
    sum = sum+val
print("The sum is", sum)

We will execute the while loop to iterate the code until the condition result is true. We will use this loop over the for loop since we are unaware of the number of iterations that will result in the code. In this example, we use while to add natural numbers up to sum = 1+2+3+...+n:

n = 10
# initialize sum and counter
sum = 0
i = 1
while i <= n:
    sum = sum + i
    i = i+1 # update counter

# print the sum
print("The sum is", sum)

The outputs for the preceding three examples are as follows:

Positive number
The sum is 83
The sum is 55
>>>