Python Loops

Python program to print multiplication table

Description: Write a Python program to print the multiplication table of a number.

Rules and hints:

• Use a for loop with range(1, 11).
• Print each line in the form 7 x 1 = 7.

Python program for multiplication table

num = 7

for i in range(1, 11):
    print(f"{num} x {i} = {num * i}")

Output:

How it works

• range(1, 11) gives the numbers 1 to 10. The end value 11 is not included.
• In each round the f-string puts the values of num, i and the product in the line.

Learn more in Python for loop.

Python program to find factorial of a number

Description: Write a Python program to find the factorial of a number using a loop.

Rules and hints:

• Factorial of 5 is 5 x 4 x 3 x 2 x 1 = 120.
• Start with 1 and multiply by each number.

Python program for factorial using a loop

num = 5
factorial = 1

for i in range(1, num + 1):
    factorial = factorial * i

print("Factorial of", num, "is", factorial)

Output:

How it works

• factorial starts with 1.
• The loop multiplies it with 1, 2, 3, 4 and 5 one by one: 1, 2, 6, 24, 120.
• For 0, the loop does not run, and the answer stays 1, which is correct.

You can also solve it with a function that calls itself. See Python Functions (recursion).

Python program to print Fibonacci series

Description: Write a Python program to print the first 10 numbers of the Fibonacci series.

Rules and hints:

• Each number is the sum of the two numbers before it.
• The series starts with 0 and 1.

Python program for Fibonacci series

a, b = 0, 1

for _ in range(10):
    print(a, end=" ")
    a, b = b, a + b

Output:

How it works

• a and b hold two neighbour numbers of the series.
• print(a, end=" ") prints on the same line with a space.
• a, b = b, a + b moves to the next pair at once.
• The loop variable _ means we do not use its value.

Python program to check prime number

Description: Write a Python program to check whether a number is prime.

Rules and hints:

• A prime number is greater than 1 and has no divisor other than 1 and itself.
• You only need to test divisors up to the square root of the number.

Python program to check a prime number

def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

for n in (2, 15, 17, 1):
    if is_prime(n):
        print(n, "is prime")
    else:
        print(n, "is not prime")

Output:

How it works

• Numbers below 2 are not prime.
• For 15 the loop tests 2 and 3. Since 15 % 3 == 0, it returns False.
• For 17 the loop tests 2, 3 and 4. None divides it, so it is prime.
• As soon as one divisor is found, return False ends the function early.

Python program to print star pattern (right triangle)

Description: Write a Python program to print a right angled triangle pattern of stars with 5 rows.

Rules and hints:

• Row 1 has one star, row 2 has two stars, and so on.
• You can repeat a string with *, like "*" * 3.

Python star pattern program

rows = 5

for i in range(1, rows + 1):
    print("*" * i)

Output:

How it works

• In round i we print the star i times.
• print() adds a new line after each row.

Related: Python Strings.

Python program to find the sum of digits of a number

Description: Write a Python program to find the sum of the digits of a number.

Rules and hints:

• Use % 10 to get the last digit.
• Use // 10 to remove the last digit.

Python program for the sum of digits

num = 1234
total = 0

while num > 0:
    total += num % 10
    num = num // 10

print("Sum of digits:", total)

Output:

How it works

• 1234 % 10 is 4, and then 1234 // 10 is 123.
• The loop continues with 123, 12 and 1, adding 3, 2 and 1.
• So the total is 4 + 3 + 2 + 1 = 10. The loop stops when the number becomes 0.

Learn more in Python While Loop.