Swap two variables in one line in C/C+

In C programming, swapping two variables means exchanging the values stored in them. There are multiple ways to implement swapping using a single line statement. This article demonstrates various approaches to swap variable values efficiently.

Syntax

// General concept
variable1 = new_value_of_variable2;
variable2 = new_value_of_variable1;

Example Scenario

Let's consider the following input and expected output −

Input:
int a = 5;
int b = 10;

Output:
a = 10
b = 5

Method 1: Using Arithmetic Operations

This method uses arithmetic operations to swap variables without temporary storage. It works only with numeric types −

#include <stdio.h>

int main() {
    int a = 5, b = 10;
    printf("Before swap: a = %d, b = %d\n", a, b);
    
    a = a + b - (b = a);
    
    printf("After swap: a = %d, b = %d\n", a, b);
    return 0;
}

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Method 2: Using XOR Bitwise Operation

This approach uses bitwise XOR operation to swap variables. It works with integer types and doesn't require temporary storage −

#include <stdio.h>

int main() {
    int a = 5, b = 10;
    printf("Before swap: a = %d, b = %d\n", a, b);
    
    a = a ^ b ^ (b = a);
    
    printf("After swap: a = %d, b = %d\n", a, b);
    return 0;
}

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Method 3: Using Comma Operator

The comma operator can be used to perform multiple operations in a single statement −

#include <stdio.h>

int main() {
    int a = 5, b = 10, temp;
    printf("Before swap: a = %d, b = %d\n", a, b);
    
    temp = a, a = b, b = temp;
    
    printf("After swap: a = %d, b = %d\n", a, b);
    return 0;
}

Before swap: a = 5, b = 10
After swap: a = 10, b = 5

Comparison

Key Points

• Arithmetic method may cause integer overflow for large values.
• XOR method is efficient but limited to integer data types.
• Comma operator method is most readable and works with all data types.

Conclusion

Single-line variable swapping in C can be achieved using arithmetic operations, XOR operations, or the comma operator. Choose the method based on your data types and readability requirements.