# @stdlib/math-base-special-roundn

0.2.1 • Public • Published

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# roundn

Round a double-precision floating-point number to the nearest multiple of 10^n.

## Installation

`npm install @stdlib/math-base-special-roundn`

## Usage

`var roundn = require( '@stdlib/math-base-special-roundn' );`

#### roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of `10^n`.

```// Round a value to 2 decimal places:
var v = roundn( 3.141592653589793, -2 );
// returns 3.14

// If n = 0, `roundn` behaves like `round`:
v = roundn( 3.141592653589793, 0 );
// returns 3.0

// Round a value to the nearest thousand:
v = roundn( 12368.0, 3 );
// returns 12000.0```

## Notes

• When operating on floating-point numbers in bases other than `2`, rounding to specified digits can be inexact. For example,

```var x = 0.2 + 0.1;
// returns 0.30000000000000004

// Should round to 0.3...
var v = roundn( x, -16 );
// returns 0.3000000000000001```

## Examples

```var randu = require( '@stdlib/random-base-randu' );
var roundn = require( '@stdlib/math-base-special-roundn' );

var x;
var n;
var v;
var i;

for ( i = 0; i < 100; i++ ) {
x = (randu()*100.0) - 50.0;
n = roundn( randu()*5.0, 0 );
v = roundn( x, -n );
console.log( 'x: %d. Number of decimals: %d. Rounded: %d.', x, n, v );
}```

## C APIs

### Usage

`#include "stdlib/math/base/special/roundn.h"`

#### stdlib_base_roundn( x, n )

Rounds a double-precision floating-point number to the nearest multiple of `10^n`.

```double y = stdlib_base_roundn( 3.14, -2 );
// returns 3.14```

The function accepts the following arguments:

• x: `[in] double` input value.
• n: `[in] int32_t` integer power of 10.
`double stdlib_base_roundn( const double x, const int32_t n );`

### Examples

```#include "stdlib/math/base/special/roundn.h"
#include <stdio.h>

int main( void ) {
const double x[] = { 3.14, -3.14, 0.0, 0.0/0.0 };

double y;
int i;
for ( i = 0; i < 4; i++ ) {
y = stdlib_base_roundn( x[ i ], -2 );
printf( "roundn(%lf) = %lf\n", x[ i ], y );
}
}```

## Notice

This package is part of stdlib, a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.

For more information on the project, filing bug reports and feature requests, and guidance on how to develop stdlib, see the main project repository.

## Package Sidebar

### Install

`npm i @stdlib/math-base-special-roundn`

### Repository

github.com/stdlib-js/math-base-special-roundn

stdlib.io

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