Question

what sequence of numbers would be printed if the following function were executed with the value of N being 0?

def xxx (N):

print (N)

if (N < 5):

xxx (N + 2)

print (N)

  

Answer 1

Considering that the function is given in the python language.

If the code layout is :

def xxx(n):
    print(n)
    if (n < 5):
        xxx(n+2)
    print(n)
xxx(0)

Then, the sequence of output would be:
0
2
4
6
6
4
2
0
Explaination of the code:
There are 2 print statements in the code, at the beginning of the function and at the end, when the function is initially called with n = 0, the first print statement executes.
Then, the if statement is checked, then the function recursively calls xxx(2), which prints 2 then it recursively calls xxx(4) which prints 4 then it recursively calls xxx(6) which prints 6. Here, the condition fails, so it exits the if condition and prints 6 and returns to the calling function (i.e xxx(4)), which prints 4 and returns to the calling function (i.e xxx(2)), which prints 2 and returns to the calling function (i.e xxx(0)) which prints 0 and returns to the main function.

If the code layout is:

def xxx(n):
    print(n)
    if (n < 5):
        xxx(n+2)
        print(n)
xxx(0)

Then Output sequence would be:
0
2
4
6
4
2
0
Explaination of this code:
This function also contains two print statements. However, the second print statement is within the if condition.
When the function xxx(0) is called initially, the first print statement executes and prints 0, then if condition is checked, which recursively calls xxx(2), which prints 2 and then recursively calls xxx(4) which prints 4 and recursively calls xxx(6) which prints 6 and the if condition fails, so it returns to the calling function (ie xxx(4)), which in turn prints 4 and returns to the calling function (ie xxx(2)) which in turn prints 2 and returns to the calling function (i.e xxx(0)) which prints 0 and returns to the main function.