Question

Suppose you want to interchange the values stored in memory cells 100 and 200. What is wrong with the following sequence of steps:

Step 1. Move the contents of cell number 100 to cell number 200.
Step 2. Move the contents of cell number 200 to cell number 100 .
Design a sequence of steps that correctly interchanges the contents of these cells. If needed, you may use additional cells.

Answer 1

To interchange the contents of memory cells 100 and 200 correctly, an additional temporary memory cell is required to hold the value during the swapping process, without overwriting the original content.

Step-by-step explanation:

The sequence provided in the question for interchanging the values stored in memory cells is incorrect because Step 1 would overwrite the content of cell number 200 with the content of cell number 100, and then Step 2 would merely move the already overwritten content back to cell number 100, leaving both cells with the content originally found in cell number 100. To correctly interchange the contents, you need to use an additional memory cell to temporarily hold the value of one of these cells during the swap process.

1. Move the contents of cell number 100 to a temporary cell (let's call it cell 300).
2. Move the contents of cell number 200 to cell number 100.
3. Move the contents of the temporary cell 300 to cell number 200.