C math.h copysign() Function

copysign() Function

The copysign() function returns a value that retains the magnitude of one operand while adopting the sign of the other. This function is useful in numerical computations where you need to control the sign of a result without modifying its absolute value.

---

Syntax of copysign()

double copysign(double x, double y);

float copysignf(float x, float y);

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

Parameters

Parameter	Description
x	Value whose magnitude is used in the resulting value.
y	Value whose sign is used in the resulting value.

Return Value

The function returns a value that has the magnitude of x and the sign of y.

The copysign() function is particularly useful when the sign of a numerical result needs to be explicitly controlled in computations without affecting the magnitude. This makes it ideal for applications involving complex numerical algorithms where sign manipulation is required.

---

Examples for copysign()

Example 1: Basic Usage to Assign a Negative Sign

This example demonstrates how copysign() is used to assign a negative sign to a positive magnitude.

Program

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

int main() {
    double magnitude = 5.0;
    double signSource = -3.0;
    
    double result = copysign(magnitude, signSource);
    printf("Result: %f\n", result);
    return 0;
}

Explanation:

1. The variable magnitude is set to 5.0, which provides the magnitude for the result.
2. The variable signSource is set to -3.0, providing the negative sign.
3. The function copysign() returns -5.0, combining the magnitude of 5.0 with the sign of -3.0.

Program Output:

Result: -5.000000

Example 2: Applying copysign() on Floating-Point Values

This example illustrates the use of copysignf() with float values to ensure the sign is transferred while the magnitude remains unchanged.

Program

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

int main() {
    float a = 7.5f;
    float b = -2.0f;
    
    float result = copysignf(a, b);
    printf("Result: %f\n", result);
    return 0;
}

Explanation:

1. The variable a is initialized with a positive float value of 7.5f.
2. The variable b is initialized with a negative float value of -2.0f.
3. The function copysignf() returns -7.5f, preserving the magnitude of a while adopting the sign of b.

Program Output:

Result: -7.500000

Example 3: Demonstrating copysignl() with Long Double Values

This example demonstrates the use of copysignl() with long double values, showing how the function transfers the sign correctly while preserving the magnitude.

Program

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

int main() {
    long double m = 12.34L;
    long double s = -0.0L;
    
    long double result = copysignl(m, s);
    printf("Result: %Lf\n", result);
    return 0;
}

Explanation:

1. The variable m is assigned a long double value of 12.34L, which sets the magnitude.
2. The variable s is assigned -0.0L to provide a negative sign.
3. The function copysignl() returns -12.34L, merging the magnitude of m with the sign of s.

Program Output:

Result: -12.340000