modf() Function

The modf() function in C splits a floating-point value into its fractional and integral parts. The integral part is stored via a pointer provided by the user while the fractional part is returned by the function. Both parts retain the same sign as the original number, making it useful in various mathematical computations where such separation is required.

Syntax of modf()

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double modf(double x, double *intpart);

Parameters

ParameterDescription
xThe floating point value to be split into its parts.
intpartPointer to an object where the integral part of x will be stored (retaining the same sign as x).

Return Value

The function returns the fractional part of given argument x, with the same sign.

It is important to note that the integral part is stored via the pointer provided, and no additional memory is allocated by modf(). Both the integral and fractional parts will share the same sign as the original value.

Examples for modf()

Example 1: Splitting a Positive Double

This example demonstrates how to use modf() to separate a positive double into its fractional and integral parts.

Program

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

int main() {
    double num = 123.456;
    double intPart;
    double fracPart;

    fracPart = modf(num, &intPart);

    printf("Fractional part: %f\n", fracPart);
    printf("Integral part: %f\n", intPart);
    return 0;
}

Explanation:

  1. A double variable num is initialized with the value 123.456.
  2. The modf() function is used to split num into its fractional and integral parts.
  3. The returned fractional part is stored in fracPart, while the integral part is stored at the location pointed to by intPart.
  4. Both parts are printed using printf().

Program Output:

Fractional part: 0.456000
Integral part: 123.000000

Example 2: Splitting a Negative Double

This example shows how modf() handles negative values by splitting a negative double into its respective parts while preserving the sign.

Program

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

int main() {
    double num = -78.910;
    double intPart;
    double fracPart;

    fracPart = modf(num, &intPart);

    printf("Fractional part: %f\n", fracPart);
    printf("Integral part: %f\n", intPart);
    return 0;
}

Explanation:

  1. The double variable num is initialized with a negative value -78.910.
  2. The modf() function splits the value into fractional and integral components.
  3. The fractional part (with a negative sign) is stored in fracPart and the integral part in intPart.
  4. The results are printed, demonstrating that the sign of both parts matches the original value.

Program Output:

Fractional part: -0.910000
Integral part: -78.000000

Example 3: Demonstrating modf() with User Input

This example demonstrates how to use modf() by accepting a floating-point number from the user, and then splitting it into its fractional and integral parts.

Program

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

int main() {
    double num, intPart, fracPart;
    
    printf("Enter a floating point number: ");
    scanf("%lf", &num);
    
    fracPart = modf(num, &intPart);
    
    printf("Fractional part: %f\n", fracPart);
    printf("Integral part: %f\n", intPart);
    return 0;
}

Explanation:

  1. The program prompts the user to enter a floating-point number.
  2. Once input is received, modf() is called to split the number into fractional and integral parts.
  3. The fractional part is returned by modf() and the integral part is stored in the variable provided via pointer.
  4. Both parts are then displayed to the user.

Program Output:

Enter a floating point number: 45.678
Fractional part: 0.678000
Integral part: 45.000000