e have discussed different approaches to swap two integers without the temporary variable. How to swap in a single line without using 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 behaviour (compiler is free to behave in any way). The reason is, modifying a variable more than once in an expression causes undefined behaviour 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 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 left operand or right operand is executed for any operator (See this for more details)
// C program to swap two variables in single line
#include <stdio.h>
int main()
{
int x = 5, y = 10;
(x ^= y), (y ^= x), (x ^= y);
printf("After Swapping values of x and y are %d %d", x,
y);
return 0;
}
Output:
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)