Evaluation of Prefix and Postfix expressions using stack

[@adityaojha2701]

You helped a lot of students achieving their goals. You deserve huge respect. Indeed.

[@HandledToaster2]

Why can't we get teachers like this in college lol. I'm sure you're tired of hearing but thank you so much for all your videos, you explain everything so well.

[@amanmishra-vt8hk]

Because Our Teachers doesn't belongs to Google. LOL

[@HandledToaster2]

@@amanmishra-vt8hk I'm sorry, I don't know what you meant to say

[@amanmishra-vt8hk]

@@HandledToaster2 He works at google.

[@HandledToaster2]

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sir i want to hug you.i watched this video and now i am certain that i will perform better in my exam

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xD but really. He's got the best lectures of DS with crystal clear explanations.

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Isn't oscar is for entertainment industry he is teaching us not entertaining, doing much greater work than entertainment

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Done

[@mohitpandey4655]

He is not alive 😭

[@bitethebyte]

You are awesome sir, You taught me the whole postfix and prefix concept in just 14 minutes including algorithm. Thank you sir

[@chirag_soni_07]

alright, please add one more thank you to your list. And sir i can't express what kind of respect you owe in every students heart.

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[@AbhishekPandey-yl3bp]

You gave strength to my self taught programming journey

[@peterwan816]

OMG thank you so much! you explained it much better than my college teacher! Thanks for sharing this valuable information with us for free! thanks a lot!

[@whacoder725]

Where u study

[@Juanbaez_]

Sir, you are the best. If you thought in a University, I would totally go there.

[@ajaychinni3148]

Even after 7 years he has the short and best video on this topic

[@HeyThereGuy]

Beautiful tutorial. Very good English. You saved me so much time.

[@laxmandora8404]

What a voice you got!!What an exaplanation skillsyou got!! Loved it

[@biswendrajonchhen124]

This is a very crystal clear explanation. Thank you for the video sir.

[@luxamateuramvs6800]

dude this is the best video i've ever watched, i totally understood everything, you are really good at teaching.

[@dragonore2009]

You saved me again, I have exam coming up where I have to evaluate these.

[@imsunilvaghela]

Hi, Your explanation skills are way greater than any of the youtuber with data-structure videos. I recommend your channel to each of my colleagues whose base seem unclear in data-structures. You have did a great job. I have one query in this lesson. How can we convert an infix expression to pre/postfix expression, which contains an unary operator in it? Please edit your video with this content or please make a separate video for this. Thanks in advance.

[@sameerahmed5078]

I heard he is no more, but he left such good videos, he lives with us as long as these videos help people like us.

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He is alive. His partner and cofounder of mycodeschool is no more. You can google for "humblefool"

[@bhagyashreekakwani9508]

Your videos help a lot in building the logic !! Thanks a lot!!

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thank you sir for such a wonderful ds experience i am seriously obliged thanks

[@dylanwatkins1158]

awesome ! so clear and understanding, thank you so much! the book for computer architecture just makes no sense. your videos are getting me through this class !

[@Camatio]

This was very helpful. You have my thanks, good sir.

[@林霈瑄]

Best version of explanation

[@rishabh8808]

You are an amazing teacher. Keep up the amazing work!

[@bahar2207]

Saved my semester. Thanks

[@vijayalakshmi8337]

It's a shame the world lost you so soon. I really wish you be reborn and teach us more.

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what happened?

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It was his friend Harsha (the co-founder of this channel) who died not him

[@mahesh-ve2bp]

There is no words to say Mind blowing explanation

[@mithileshpandit1071]

too OP man... You are the best teacher on the planet

[@AnilSingh-rg2eq]

sweet and simple...u make concepts looks so simple..Thanks a lot :)

[@ryanyoung2583]

This is so well done. Thank you so much for creating these videos.

[@563woodcock]

A small correction in your code.... In else if(IsNumericDigit(expression[i])) don't do int operand = 0; Remove this line otherwise every time the control enters this else if statement it will assign the index of the string to 0 and start reading from the very beginning of the string.

[@ankitajain4194]

It will be really good if you can explain Time and space complexity too with your videos.

[@kumarpriyansh4238]

awesome. Very clear explanation sir.Understood it totally

[@ahmedsoliman4015]

Thank you! an awesomely detailed explanation, and the visualization was very informative too!

[@tanishkaachaturvedi2173]

best video on the internet

[@theneonlotus]

great video, very clear description of pre and post fix. found it very useful

[@lordstinson8095]

Great video! How do we evaluate prefix/postfix expressions in case of *unary operators* ?

[@dumdumbringgumgum2940]

in case of prefix the operand immediately succeeding the unary operator. and in case of postfix. the operand immediately preceding the unary operator.

[@buddhiniwalakuluarachchi8281]

thank sir.. this is best video for post-fix which i met

[@AkGautam_1904]

Awesome explanation ❤️. Thank you sir 🤩🤩✨.

[@mato4430]

You are absolutely genius

[@ManojChausali]

Program for prefix evaluation #include #include #include using namespace std; bool isOperand(char C) { if(C>='0' && C

[@culturapoliticaycomputador9999]

Amazing, thank you so much, for this kind of video. God bless you sir.

[@amanmalhotra724]

fab u all did a fab job awesome explanations this has become one of my fav site and videos thanks and keep it up u guys

[@jangandilogout8653]

Big thanks sir. Very helpful for my exam 😍

[@shaikgousiya2151]

You are a good teacher

[@thatoneuser8600]

10:48 shouldn't it be 9 - 26 which would be -17? I don't understand which operand is the leader when it comes to subtraction.

[@earthisadinosaur2338]

truly a godly video my dude

[@moazelsawaf2000]

Really thanks a lot sir

[@imjustjoshying]

Nice Video but you made a mistake in the video during "prefix" notation. You popped 5 & 4 and you multiplied them even though the symbol was + addition.

[@SandeepVerma1429]

printing mistake dear...

[@btsarmyonly5774]

Good explanation sir... Thank you so muchhh

[@rohananjaria1009]

Code for prefix evaluation #include #include #include using namespace std; // Function to evaluate Porefix expression and return output int EvaluatePrefix(string expression); // Function to perform an operation and return output. int PerformOperation(char operation, int operand1, int operand2); // Function to verify whether a character is operator symbol or not. bool IsOperator(char C); // Function to verify whether a character is numeric digit. bool IsNumericDigit(char C); int main() { string expression; cout

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[@PiyushYadav-hf1ec]

Great Explanation👍🏻👍🏻👍🏻👍🏻

[@narmadapasumarthi9190]

Really excellent explanation. Thank you very much..

[@taimoorsk]

Great teacher 😍😍

[@tree78254]

In evaluation of prefix exp, atlast... If d operator comes, u hav two pop two elements...n here 2nd element is the 2nd operand.. So d final ans should be like -17 right???

[@lagend0066]

thanks a lot for so much easy method .....GOD bless you man

[@Klish47]

amazing..thanku sooo muchh... understood like never before

[@AmrendraKumar-ko8yf]

yeah ..absolutely So, what r u doing these days . job or studying

[@shivanshmathur403]

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[@udz26]

The prefix expression -+*23+549 is evaluating to 6, not 17... I even checked on online prefix analyzers. Correct me if I am wrong, Edit: Please ignore this, the actual expression is -+*23*549.

[@manistrikes]

Well after 23 it's the multiplication operator and not '+'.

[@udz26]

@@manistrikes Ohh god... and I was frustrated over why my answer is not 17 🤦🤦🤦

[@yogieanugrah3865]

Thanks! you helped me get my homework done. :)

[@amanmishra-vt8hk]

By the way answer should for the prefix be 6. If I am wrong please correct me.

[@ericnelsonelem5241]

Very illustrative. Thank you!

[@eldadkanawa6527]

Nice Explanation, Thanks a lot

[@gmunni17]

for the prefix example, could you not write it as: - 9 + * 5 4 * 2 3 this gives me the same final answer of 17

[@MYtantrums]

on evaluation of postfix, which one did u pop first? 26 or 9, since OP1 should be 9 because it is the first one to pop and OP2 is 26 (following LIFO), please clarify

[@jeetbardapurkar4912]

9 was the first to pop and then 26 was popped. The way he has programmed, op2 holds the value of the element which was popped first and op1 holds the value of the element popped later. You can interchange what op1 and op2 mean when you write your own code.

[@iam_a_sad_khan]

I also got confused first but look 9 pops out first as op2 and then 26 pops out as op1. Now perform the operation op1- op2 that is 26- 9. I hope that makes sense.

[@DarkLordAli95]

thank you so much kumar.

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[@BladeAndrade]

why at the subtraction you place 26 as operand 1 instead of 9? isn't supposed to pop the topmost elements of the stack? 9 is the topmost and must pop out first then 26 so you will have 9-26, I'm confused.

[@yashmehan3944]

very well explained, thank you very much!

[@dearvivekkumar]

Great explanation as always

[@harshmairh495]

thank u for this amazing video. u r doing a great job!!

[@redmood1097]

Thank you very much it was very helpful .

[@tigershroff8026]

4:01 there is a mistake. The stack is 26 9 - at the end. It should be popped as 9 - 26 = -17 but it is popped as 26 - 9 = 17. Am I right?

[@golubhai1910]

getting answer 9 from your source code.

[@rztutul8824]

just awesome explanation ....Tnx

[@vengtCent]

Great explanation!

[@meenugabalachandra325]

answer may me -17 because last last stage 9,26 are in the stack so 9-26=-17

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You were a genius,no wonder!

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[@abhishekkumar-so7ww]

you have got good vocal cords

[@5thbatman]

great explanation...

[@bolu3307]

Python implementation of postfix expression evaluation. Note: Parses single-digit numbers only. You may implement your preferred parser for input. #Stack class implementation class stack(): def __init__(self): self.headNode = None def trav(self): if(self.headNode): checkNode = self.headNode print checkNode.data while checkNode.next: next = checkNode.next print next.data checkNode = next def push(self,val): NN = Node(val) NN.next = self.headNode self.headNode = NN def pop(self): if(not self.headNode): return None CNode = self.headNode self.headNode = self.headNode.next return CNode def not_emp(self): if(self.headNode!=None): return True return False def top(self): return self.headNode #import operator module to match operator characters with Arithmetic functions import operator def postfix_eval(exp): #operator dictionary, pairing characters with arithmetic functions operators = {"+":operator.add,"-":operator.sub,"*":operator.mul,"/":operator.div} exp_stack = stack() for i in exp: #if not operator, i.e if operand, add to top of stack if(not i in operators): exp_stack.push(i) else: #if character operator, pop last two top elements in stack, be mindful of the order operand2 = int(exp_stack.pop().data) operand1 = int(exp_stack.pop().data) #call arithmetic operator with character as key in operators dictionary, and pass the last two popped elements as parameters result = operators[i](operand1,operand2) exp_stack.push(result) #when all done, return top(only) element left in stack return exp_stack.pop().data

[@MegaBdboy]

What code should i write to evaluate the expression from right ?

[@tune_into_gaming]

best explanation...

[@shamim-io]

Thanks.. Helped me a lot!!

[@nabilaaziz3446]

Good job!! Great explanation. thanks :)

[@whacoder725]

I have tried 3 days to solve this question but i can't why it is showing null value

[@TechnoForbes]

Awesome Explanation .. Thanks a Lot :)

[@niamatullahbakhshi9371]

in 13:16 , it was addition(+) but you multiplied however multiplication has not reached ! why ?

[@ashutoshsingh419]

thanks so much for this explanation

[@himanshugupte5543]

You guys are awesome!

[@dragansmoljan7917]

what if i want to write an expression without spaces or comas? 2+3*4-5? i get a error, i dont know why

[@ankitjangid1]

Sir can you please tell how to convert complex expressions into postfix, for ex :- in my book a question is given i.e A*(B+D)/E-F-(G+H/K) and (A+ B ^ D)/(E-F)+G (^ IS NOT POWER). Please help!!

[@jameslussier3143]

this was very helpful, thanks a lot

[@sunandareddy5126]

Evaluate the following prefix expression " ++ 26 + - 1324" sir can u plz explain

[@aliesapour79]

Thank you so much for your video

[@tomlynd8836]

Awesome explanation, thanks!

[@mairaabid4538]

if statement is that ( a=b=x=y=0) so what we do in postfix and prefix?

[@andreasan1783]

thanks, very helpful