Swap two variables in one line
We have discussed different approaches to swap two integers without the temporary variable. How to swap into a single line without using the library function?
Python: In Python, there is a simple and syntactically neat construct to swap variables, we just need to write “x, y = y, x”.
C/C++: Below is one generally provided classical solution
// Swap using bitwise XOR (Wrong Solution in C/C++) x ^= y ^= x ^= y;
The above solution is wrong in C/C++ as it causes undefined behavior (the compiler is free to behave in any way). The reason is, modifying a variable more than once in an expression causes undefined behavior if there is no sequence point between the modifications.
However, we can use a comma to introduce sequence points. So the modified solution is
// Swap using bitwise XOR (Correct Solution in C/C++) // sequence point introduced using comma. (x ^= y), (y ^= x), (x ^= y);
Java: In Java, rules for subexpression evaluations are clearly defined. The left-hand operand is always evaluated before the right-hand operand (See this for more details). In Java, the expression “x ^= y ^= x ^= y;” doesn’t produce the correct result according to Java rules. It makes x = 0. However, we can use “x = x ^ y ^ (y = x);” Note the expressions are evaluated from left to right. If x = 5 and y = 10 initially, the expression is equivalent to “x = 5 ^ 10 ^ (y = 5);”. Note that we can’t use this in C/C++ as in C/C++, it is not defined whether the left operand or right operand is executed by any operator (See this for more details).
After Swapping values of x and y are 10 5
Alternate Solutions :
- C++ also provides a library function swap()
- b = (a + b) – (a = b); [Thanks to Rajat Mishra for this]
- a += b – (b = a); [Thanks to Zoran Davidovi? for this]
- a = a * b / (b = a)[Thanks to kongasricharan for this]
- a = a ^ b ^ (b = a)
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