Section 1.29 Worked Example: Swap
Subgoals for evaluating an assignment statement.
- Determine resultant data type of expression
- Update variable for pre operators based on side effect
- Solve arithmetic equation, operator precedence
- If = statement, is Left Hand Side (LHS) a variable? Check data type of copied value against data type of variable
- Update variable for post operators based on side effect
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Consider these declarations.
int x,y,z; x = 7; y = 13;
Now consider this code for swapping the values of x and y. Note the need for a third variable to hold the value of x so that it is not lost when assigning the value of y into x.
z = x; x = y; y = z;
The diagram below shows the changes in memory after executing each of the six lines of code.
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