Practice question

Duration: 2 min

This video lesson is available to enrolled students.

Enroll to watch — ISRO Scientist/Engineer 'SC'

AI Summary

An AI-generated summary of this video lecture.

The video presents a computer science problem regarding memory address calculation for arrays with non-zero or negative lower bounds. The instructor explains how to determine the memory address of a specific element when the array declaration starts at a negative index. Key parameters provided include the array range from -6 to 6, the element size of 4 bytes, and a base address of 3500. The core concept involves applying a specific formula that accounts for the offset from the lower bound rather than just the index itself. This is crucial for understanding how compilers allocate memory for arrays that do not start at index 0. The problem is clearly written in orange text at the top of the slide.

Chapters

  1. 0:00 – 1:47 00:00-01:47

    The instructor begins by displaying a problem statement on the screen: "An array has been declared as follows A: array [-6-------6] of elements where every element takes 4 bytes, if the base address of the array is 3500 find the address of array[0]?" He identifies the Lower Bound (LB) as -6 and the Upper Bound (UB) as 6, writing these labels in red ink above the numbers. He notes the word size w=4 bytes. He then writes the general address calculation formula: a[K] = B + w * [K - LB]. He defines B as the base address. He substitutes the given values into this equation: Base Address B=3500, target index K=0, and LB=-6. The calculation proceeds as 3500 + 4 * [0 - (-6)], which simplifies to 3500 + 4 * 6. This results in 3500 + 24. Finally, he writes the result 3524 and underlines it in red ink as the final solution.

This lesson demonstrates the critical distinction between standard array indexing and arrays with arbitrary lower bounds. By using the formula Address = Base + WordSize * (Index - LowerBound), the instructor shows that the memory address is relative to the start of the allocated block, not index zero. This ensures correct memory access even when indices are negative, a common scenario in languages like Pascal or C with pointer arithmetic. Understanding this offset mechanism is fundamental for low-level programming and memory management tasks.