The copysign() function in C is part of the standard math library <math.h> and is used to create a floating-point number that combines the magnitude of one number with the sign of another. It copies the sign from one floating-point number and applies it to the magnitude of another floating-point number.

In this article, we will learn about the copysign() function in C and

Syntax of copysign() in C

double copysign(double x, double y);

Parameter

The copysign() function in C takes the following parameters:

• x: The value whose magnitude is to be used.
• y: The value whose sign is to be copied.

Return Value

The copysign() function returns a value that has the same magnitude as x but the sign of y.

Variants of copysign() in C

Apart from the standard copysign() function, there are two more variants of the copysign() function, based on the type of floating-point numbers:

copysignf() for float

float copysignf(float x, float y);

copysignl() for long double

long double copysignl(long double x, long double y);

Note: The operation performed by copysign is at the bit level, making it both efficient and reliable.

Examples of copysign() Function in C Language

Example 1: Program to demonstrate how to use the copysign() function

// C Program to demonstrate the copysign() function

#include <math.h>
#include <stdio.h>

int main() {
    double x = 10.5, y = -5.5;
    double result = copysign(x, y);

    // Print the result
    printf("The value with magnitude %.2lf and sign %.2lf is: %.2lf\n", x, y, result);

    return 0;
}

The value with magnitude 10.50 and sign -5.50 is: -10.50

Time Complexity: O(1)
Auxiliary Space: O(1)

Example 2: Program to demonstrate how to use the variants of copysign()

// C program to demonstrate the copysign() function for
// different data types

#include <math.h>
#include <stdio.h>

int main()
{
    double x1 = 10.5, y1 = -5.5;
    float x2 = 20.5f, y2 = -6.5f;
    long double x3 = 30.5l, y3 = -7.5l;

    // copysign function for double
    double result1 = copysign(x1, y1);

    // copysignf function for float
    float result2 = copysignf(x2, y2);

    // copysignl function for long double
    long double result3 = copysignl(x3, y3);

    // Print the results
    printf("The value with magnitude %.2lf and sign %.2lf "
           "is: %.2lf\n",
           x1, y1, result1);
    printf("The value with magnitude %.2f and sign %.2f "
           "is: %.2f\n",
           x2, y2, result2);
    printf("The value with magnitude %.2Lf and sign %.2Lf "
           "is: %.2Lf\n",
           x3, y3, result3);

    return 0;
}

The value with magnitude 10.50 and sign -5.50 is: -10.50
The value with magnitude 20.50 and sign -6.50 is: -20.50
The value with magnitude 30.50 and sign -7.50 is: -30.50

Time Complexity: O(1)
Auxiliary Space: O(1)

Practical Applications of copysign() Function

The copysign() function is particularly useful in various scenarios, such as:

• When performing complex calculations, ensuring the correct sign of intermediate results can be crucial.
• In computer graphics and physical simulations, vectors and forces often need to be manipulated with specific signs.
• Copying signs can be important when dealing with waveforms and other signals in signal processing.