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Stack & queue
Stacks are data structures that follow LIFO (last in, first out) ordering. Elements can only be added to or removed from one end, called the top. Stacks are used to maintain information between main programs and subroutines. Elements are pushed onto the stack by decrementing the stack pointer and storing the element, and popped off by incrementing the stack pointer after retrieving the element. Operations must check that the stack is not empty before popping or full before pushing to prevent errors.
In this document
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Introduction to stacks and queues, role in subroutine structure, and information maintenance.
Explanation of stacks, characteristics, and top/bottom structure.
Applications of stacks in image processing, pattern retrieval, and parallel processing.
LIFO principle, push and pop operations, and memory address management in stacks.
Illustration of stack in memory, including numerical values and stack pointer.
Detailed push operation steps with instructions on moving items to the stack.
Detailed pop operation steps with instructions for retrieving top item from stack.
Memory allocation for stacks, importance of avoiding overflow and underflow conditions.
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Stack & queue
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- 2. A computer oftenneed to perform a particular subtask using the familiar subroutine structure. In order to maintain information and linkage between main program and subroutine, a data structure called stack is used.
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- 4. STACK Astack is a list of data elements, usually words or bytes, with accessing restriction that elements can be added (or) removed at one end of the list is called top of the stack. Other end is called bottom of the stack. The structure is sometimes referred to as a pushdown stack.
- 5. Example Image processing Pattern retrieval Parallel processing
- 6. Another descriptive LIFO-thelast data placed on the stack is the first one removed when retrieval begins. Push & Pop- used to placing a new item on the stack and removing the top item from the stack.
- 7. Assume data storedin stack First element is placed in location BOTTOM, when new elements are pushed onto the stack, they are store successive lower address locations. We use a stack that grows in the direction of decreasing memory addresses.
- 8. example Stack ofword items in the memory of a computer. It contain numerical values, with 43 at the bottom and -28 at the top. SP- A processor register point the top of the stack. 32 bit word length and byte addressable.
- 10. Push operation Subtract#4, SP Move NEWITEM, (SP) The subtract instruction subtracts the source operand 4 from the destination operand contained in SP and place the result in SP. These two instructions move the word from location NEWITEM onto the top of the stack, by decrementing the stack pointer by 4 before the move.
- 12. POP operation Move (SP), ITEM Add #4,SP These two instruction move the top value from stack into location ITEM and then increment the stack pointer by 4, now SP point to the new top element.
- 13. Auto increment ordecrement Move NEWITEM, -(SP) -Push operation Move (SP)+, ITEM - POP operation
- 14. concept When stackis used in a program, it is usually allocated a fixed amount of space in the memory. We must avoid push an item onto the stack when the stack has reached its max size. We also avoid pop an item when the stack off an empty stack. Which could result from a programming error.
- 15. example Stack runsfrom location – 2000(Bottom) And no further than location 1500 Recall that SP is decremented by 4 before new data are stored on the stack. Hence, an initial value of 2004 means that the first item pushed onto the stack will be at location 2000.
- 16. Prevent push orpop on empty stack