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lecture_12 - ECE 190 Lecture 12 Stack Lecture Topics Stack...

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ECE 190 Lecture 12 September 29, 2011 1 V. Kindratenko Stack Lecture Topics Stack data structure Lecture materials Textbook Ch. 10 Homework/Projects MP2.1 is out, due next Wednesday Announcements Exams will be available for pickup during the labs on Friday
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ECE 190 Lecture 12 September 29, 2011 2 V. Kindratenko Stack concept Stack is an abstract data type that finds many uses Stack of books example o A new book always goes on top of the stack o We can only remove a book from the top of the stack Item (book) put last onto the stack of other items (books) will be the first item removed from the stack o Last In First Out (LIFO) Coin holder example: true mechanical stack implementation o First coin in is the last coin out Stack terminology o We say we push an element onto the stack when we add to the stack o We say we pop an element from the stack when we remove from the stack Stack implementation requires 4 operations o Push to add to the stack o Pop to remove from the stack o IsEmpty to check if the stack is empty o IsFull to check if the stack is full Conceptual hardware implementation 1995 1996 1998 1982 1995 1998 1982 1995 Initial State After One Push After Three More Pushes After One Pop / / / / / / / / / / / / / / / / / / / / / / / / / / / / / / Yes Empty: TOP #18 / / / / / / / / / / / / / / / / / / / / / / / / No Empty: TOP #12 #5 #31 #18 / / / / / / No Empty: TOP #31 #18 / / / / / / / / / / / / / / / / / / No Empty: Initial State After One Push After Three More Pushes After Two Pops
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ECE 190 Lecture 12 September 29, 2011 3 V. Kindratenko o Each time we push a new element onto the stack, we need to copy all the elements that are already in the stack to make space on top of the stack for the new element Not efficient A better way is to keep the elements “stationary”, and just move the pointer to the top of the stack o By convention, R6 holds the top of stack pointer o
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