CODEWITHSUNDEEP
pythonif-statementmodulus
rupakk
rupakk

Reputation: 27

Why does the second program work but not the first?

First :

a = int(input())
if a%4 == 0:
    a += 1
if a%4 != 0:
    a -= 1
print(a)

Second :

a = int(input())
b = a%4
if b == 0:
    a += 1
if b != 0:
    a -= 1
print(a)

Upvotes: 1

Views: 53

Answers (1)

trincot
trincot

Reputation: 350345

The first will have possibly modified a before the second if condition is evaluated, and so behaves differently:

if a%4 == 0:
    a += 1 # this influences the result of the next IF
if a%4 != 0:
    a -= 1

In fact, in this particular case, if the first condition is true, then after 1 is added to a, the second condition will also be true, and so a gets 1 deducted from it again.

The second version first stores in b the result needed for the conditions to work on the original input value, and only then performs the modification of a, which is no longer playing a role in the if conditions. There, it is guaranteed that only one of the two if conditions is true.

However, most would just use else, which removes this problem:

if a%4 == 0:
    a += 1
else:
    a -= 1

Upvotes: 8

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