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Python Program to Find Factorial of a Number Using For Loop & Recursion Tutorial For Beginners
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Jun 1, 2025
Get the full source code of application here:
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0:00
uh hello guys uh welcome to this video
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uh so in this video I will show you a
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very famous program which is asked
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inside interview or competitive
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programming which is called as factorial
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program inside Python i will show you
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both the techniques using uh a for loop
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or the technique of recursion or calling
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the same function again and again to
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calculate the factorial of a number
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so factorial is a
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uh basically we calculate factorial if
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you want to calculate factorial of five
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we say 5 * 4 * 3 * 2 * 1 so this is the
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concept of
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factorial so this is uh I will show both
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the uh codes here for for loop so let's
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suppose I show you first of all the for
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loop so I'm just using this website
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pythonutor.com which actually shows the
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realtime execution of the program so
1:00
this is a great tool where you can
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visualize the source code how it is
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executed so let me first of all write
1:08
the program so we declare a
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function factorial iterative and inside
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this we will receive an argument of
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n so we declared this function so as you
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can see we are receiving this number as
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an argument so now to calculate the
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factorial we need a variable of result i
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will initialize this variable to one and
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then we will put a for loop which will
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run
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from 1 up
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till n
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so for this in Python what this works is
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it will if the value of n is five so it
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will run from 1 to
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uh five so this is how which so the
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initial value of i is equal to 1 and if
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the value of n is let's suppose five so
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it will stop at five itself so this
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value is not ex it it is not included so
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it will run up till 1
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to5 so I will explain you when I uh
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visualize this program using this tool
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so now in the factorial program we
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simply multiply the number so we simply
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say result multiplied by whatever is the
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value of i and then lastly we return the
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result that's
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all and now we simply first of all take
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the number from the
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Using the integer we type cast
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it we use the input function to receive
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the value so here we will simply ask the
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user to enter a number so here the user
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will enter the number and then we will
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print out we will call this
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function and just display the result so
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we are calling this function so if I
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execute uh click this button of
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visualize execution so now step by step
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just see how the code is executing so if
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I show you first of all this function is
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registered in the global
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frame this is your function and then
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here it
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actually ask enter a number so I will
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enter five here and click on submit so
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now the initial value of number is five
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so now this value is passed here if I go
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to the next step so this function is
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defined using this n value is five here
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if you see n value is five and now if I
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go to the next step so it basically
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initializes result to one so as you can
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see result is equal to 1
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and then in the next step we initialize
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this for loop as you can see the initial
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value of I is set to one so the initial
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value of I is equal to 1 and then we
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multiply whatever is the
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result var variable was 1 so 1
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multiplied by 1 comes out to be 1 so we
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come to the next iteration when I
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becomes two so now the i value will
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become two so 2 * 1 because result is
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equal to 1 so which will be comes out to
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be two so as you can see now I becomes
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two here so 2 * 1 so result also becomes
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two so as you can see and now we come to
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the next step now i becomes
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three so in the next iteration I becomes
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three so 3 * 2 so this will become six
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so as you can see now the result value
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becomes six so now in the next iteration
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I will be incremented furthermore I will
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become four so 4 * 6 comes out to be 24
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so as you can
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see now I become 5 the next
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iteration again we multiplied 5
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multiplied by 24 this time so it comes
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out to be 120 and now I become six so
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six is not included here so as soon as
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the program hits this the for loop will
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break and now we will come to this step
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return result so now we come to this and
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now your return value is 120 and that's
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all after that we print out this in the
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next step so now the program ends we
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display the factorial comes out to be
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120 so this is a very easy program in
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this we use the for loop very
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easily and now I will be showing you the
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second approach by which you can achieve
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it the concept of recursion recursion is
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the way by which we actually call the
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same function again and again so let's
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suppose I define this function here
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so this is your recursive function and
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here we will put a end condition as well
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because in recursive function you do
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need to put it this condition because if
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you don't put this condition the program
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will run endless number of time so we do
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need to put this condition that if n
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becomes zero or if n becomes one in
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either of these cases we need to return
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a one and
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just end this but up till now if n is
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not equal to zero or one in that case we
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need to multiply n multiplied by and
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then we need to call the same function
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again here and this time n minus
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one so we are following the same
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technique here if you want to calculate
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the factorial of five so we simply say 5
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* again we call the same function so 5 -
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4 so like this so 5 4 * 3 so this is the
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same technique that we are using and
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again let me show you how it executes
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step by step
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so again we simply take the user input
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using the input function and then we
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print out the factorial so now if I
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click the visualize execution so now
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what happens right here if you see first
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of all the function is
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registered in the global frame here the
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function is registered now we need to
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say again if I print out number here we
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need to submit so now
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the function is initialized here you can
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see factorial num is five if I go to the
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next step the function is registered
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with n is equal to 5 and then I come to
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the next step this if condition so the n
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value is five here so it is not equal to
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zero so this will fail here and then we
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come to this step so 5
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* and this value will be four 5 - 1 so
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now the n value become four here as you
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can
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see so this stays here so 5 multiplied
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by and we are again calling the same
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function but this time it is four and
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then we come to this again this
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condition will fail and
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now n value is four so four multiplied
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by again we call the same function now
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the value will become three can
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see can see that again we come same
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condition hits now it will become two as
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you can see so these are recursive
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functions guys as you can see these are
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recursive
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functions and we are waiting for the
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condition when be n becomes one so now
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again we check we n is not equal to 1 so
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we again come and this time n will
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become one so now this condition is now
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met here and now again if I check for
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this condition so now n has become one
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so in this case the condition will
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evaluate to true and now we will be
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returning one so now what happens if I
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click next
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again so this return one statement will
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execute and now your return value is
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there so now return values come so 1
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multiplied by again we need to execute
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the previous recursive functions which
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were not executed so 1 multiplied by two
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so this will comes out to be return
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value
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two so this is happening internally as
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the condition has met now so now this
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return value has this function is
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executed now this return value will
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transfer to the next recursive function
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so 2 * 3 comes out to be six so as you
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can see so now 6 * 4 comes out to be 24
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so as you can see now 24 * 5 which is
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120 at last recursive function that's
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all so this is your return value and if
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I click next and now your factorial has
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been printed out so both these
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approaches guys I showed you for loop
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and recursion i personally like this
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program which is recursion because it's
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short concise and also it is following
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the concept of recursion which is a good
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programming concept in which you execute
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the same function again and again to
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basically break the problem into
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multiple parts and then execute this so
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these are the two programs which are
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asked come specifically in interviews
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whenever you go for interview or
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competitive programming and thank you
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very much guys for watching this video
11:27
also check out my website
11:28
freemediattools.com
11:30
uh which contains thousands of tools
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