t=x;x=y;y=t;

These three lines of code are used to swap the values of two variables, x and y.

The first line assigns the value of x to a temporary variable t. The second line assigns the value of y to x, effectively swapping the value of x with y. The third line assigns the value of t (which is the original value of x) to y, completing the swap of values between x and y.

After these three lines of code are executed, the values of x and y will have been swapped.