Python Forum

I don't know why the output of these two programs is different
1.

Number=123
Reverse = 0    
while(Number > 0):    
    Reminder = Number %10    
    Reverse*=10 + Reminder    
    Number = Number //10   
print(Reverse)

Output:
0

2.

Number=123
Reverse = 0    
while(Number > 0):    
    Reminder = Number %10    
    Reverse=Reverse*10 + Reminder    
    Number = Number //10   
print(Reverse)

Output:
321

This gets a little deep, but you need to read about inplace operators in the Python docs. The problem is that the assignment to Reverse (btw - don't use capitals for the first letter in variable names, see PEP 8) occurs BEFORE the addition. So, it stays 0. If you then separate the operations it works.

Number=123
Reverse = 0    
while(Number > 0):    
    Reminder = Number %10    
    Reverse*=10
    Reverse+=Reminder
    print(Reverse)    
    Number = Number //10   
print(Reverse)

Output:
3
32
321
321

from the docs:

Quote:Unlike normal assignments, augmented assignments evaluate the left-hand side before evaluating the right-hand side. For example, a[i] += f(x) first looks-up a[i], then it evaluates f(x) and performs the addition, and lastly, it writes the result back to a[i].

so, in the first snippet:

reminder *= 10 + reminder

is same as

reminder = reminder * (10 + reminder)

and reminder always stays 0