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How to Reverse Digits of a Number Using While Loop in Python – GATE, Interview & Placement Practice
Jun 1, 2025
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0:00
uh hello guys welcome to this video so
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in this video I will show you a very
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common program which is asked inside uh
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coding interviews and competitive exams
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such as GATE or placements which is how
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to reverse a number inside Python so
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this is actually essentially the program
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right here if I execute this it will ask
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you to enter a number you can write any
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number let's suppose I write uh 5 6 7
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this is the number that I write here so
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what will be the output so what this
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program will do it will reverse all the
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digits of this number which output will
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be
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765 so as I enter it you will see
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reverse of this number is 765 so how to
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calculate the reverse i will show you in
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this video this is a simple logic using
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while loop we are using while loop here
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so let me just paste this program in a
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software called as Python tutor which
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will show you step by step how this
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program executes line by line so let me
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paste it and visualize execution so now
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the very first step right here it is
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asking you to enter the number so if I
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write here
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45 6 and click on submit and you can see
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we have declared a global variable which
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is
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456 now we need to reverse this number
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and print out
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654 this is our task so now to do this
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we actually declare a brand new variable
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which will be called as reverse and it's
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in initialized to zero so now a new
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variable has been declared which is
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reverse which is set to zero and for
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this we are having this while
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loop we are using the while loop here
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while n is greater than
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zero in this scenario you will see n is
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456 it is greater than zero so this
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condition will evaluate to true and now
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the control will shift to the center of
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the loop
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so the very first step right here what
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we are doing we are dividing this number
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by 10 whatever is the number which is 4
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5
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6 so we are dividing it by 10 and
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whatever is the remainder comes out to
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be so we know
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that the remainder will be six
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so what will be the output here which
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will be stored inside this remainder
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variable which will be six so now you
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can
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see now we extracted the last digit
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right here and printed out in the front
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so this is the way and now in the next
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step
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we update this value of
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reverse and what we do right here we
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divide uh sorry multiply this number by
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10 and add whatever is the remainder
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there
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so right here reverse is 0 so 0 *
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6 0 * 10 comes out to be 0 and whatever
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is the remainder is 6 so its value will
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also change to six so now if you see it
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also becomes
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six and now we divide this number by 10
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so this division operator is different
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this will not catch the remainder this
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will only divide the number by 10 so if
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you divide this by 10
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again so it comes out to be 45 and this
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six will be removed so now it becomes 45
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now you can see that again we repeat
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this process 45 is greater than zero
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again we divide this number by 10
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so we say 10 4 are 40 and we get
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remainder once again of five it's a very
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simple process how we extract the last
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digit just divide the number by 10 and
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get the remainder now we'll be shifting
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this value to this one so again
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we put this value now this will make the
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remainder to five so again we do we
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multiply
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this reverse whatever is present we
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multiply this by 10 so 6 10 are 60 and
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then whatever is the remainder is there
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which is 60 + 5 and it comes out to be
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65 so as you can see so now once again
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we divide this number by 10 so we remove
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this so now this will be four again
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control shift again four is greater than
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zero again we divide this by 10 and the
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remainder will be zero
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now so now this will become four sorry
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this will become four because if you
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divide
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by so you will
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see remainder comes out to be four so
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now it is four
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so again now in the next
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step we multiply this by 10 so it comes
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out to be
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650 +
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4 so now the output is
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654 so that's all we reverse the number
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and uh
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now n is we again divide this by
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10 so it comes out to be zero and uh n
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becomes zero so this condition will
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evaluates to false so we will break out
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from the loop and simply print out the
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reverse number is
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654 so this is a very simple three-step
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logic if you want to reverse all the
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digits inside the number first of all
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you divide the number and catch the
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remainder and then you multiply
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remainder you multiply whatever is the
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reverse so we declared this reverse
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variable that's why we declared this to
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store
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this so I showed you step by step in
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this way you can reverse the number
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using while loop uh please hit that like
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button subscribe the channel and also
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check out my website freemediatools.com
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uh which contains thousands of tools
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