How Can I Efficiently Round Up Numbers to the Nearest Multiple in C ?

Rounding Up to a Multiple of a Number in C

When working with numbers in programming, it can be necessary to round up values to the nearest multiple of another number. There are multiple ways to approach this task in C , but this article will focus on an efficient method that leverages integer arithmetic to achieve accurate rounding.

The provided code snippet, roundUp, offers a straightforward solution for positive numbers. It calculates the remainder when the input number numToRound is divided by the multiple and adds the multiple to numToRound if the remainder is non-zero. This ensures that the result is the closest multiple that is greater than or equal to the input.

However, for negative numbers, the original code doesn't provide the desired behavior. To accommodate negative numbers, a modified version of roundUp is introduced. This version calculates the absolute value of the input number before performing the rounding operation. Additionally, it employs conditional logic to adjust the sign of the result based on the sign of the input. This ensures that the result is always greater than or equal to the input, regardless of its sign.

Here's the updated code for handling both positive and negative numbers:

int roundUp(int numToRound, int multiple)
{
    if (multiple == 0)
        return numToRound;

    int remainder = abs(numToRound) % multiple;
    if (remainder == 0)
        return numToRound;

    if (numToRound < 0)
        return -(abs(numToRound) - remainder);
    else
        return numToRound + multiple - remainder;
}

Now, the roundUp function provides consistent behavior for both positive and negative inputs, ensuring accurate rounding to the nearest multiple of a given number.

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