Question 25 - Sample Paper 2 by Teachoo - Teachoo Sample Paper

Predict the output of the following code:

def sum(n):

    if n == 0:

        return 0

    else:

        return n + sum(n-1)

x = 5

y = sum(x)

print(y)

x = sum(x-2)

print(x, end='!')

Answer:

Answer by student

The output is:

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15

6!

Detailed answer by teachoo

• The code defines a recursive function named sum that takes a parameter n and returns the sum of the first n natural numbers.
• A recursive function is a function that calls itself within its body, until a base case is reached.
• The base case for this function is when n is 0, in which case it returns 0.
• The recursive case is when n is greater than 0, in which case it returns n + sum(n-1) , which means adding the current number to the sum of the previous numbers.
• The code then assigns 5 to a variable x and calls the function sum with x as an argument, storing the result in a variable y .
• The function call sum(5) will return 15 , which is 1 + 2 + 3 + 4 + 5, and this value will be assigned to y .
• The code then prints the value of y , which is 15, followed by a newline character.
• The code then calls the function sum again with x-2 ie., 5-2 = 3 as an argument, and assigns the result to x .
• The function call sum(x-2) will return 6, which is 1 + 2 + 3 , and this value will be assigned to x .
• The code then prints the value of x , which is 6, followed by an exclamation mark and no newline character.

So, the output of the code is:

15

6!

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