Rob Cook


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Fizz Buzz


2021-03-02

The programmer's Stairway to Heaven, there is no escaping Fizz Buzz. Cropping up in interviews everywhere, it's also a useful little task to write when learning a new language. This has the added benefit of potentially changing how you look at the problem.

My usual C# solution is very straightforward.


public static string FizzBuzz(int num)
{
    var divBy3 = num % 3 == 0;
    var divBy5 = num % 5 == 0;
    string word;
    
    if (divBy3 && divBy5)
    {
         word = "FizzBuzz";
    }
    else if (divBy3)
    {
        word = "Fizz";
    }
    else if (divBy5)
    {
        word = "Buzz";
    }
    else
    {
        word = num.ToString();
    }
    
    return word;
}

public static void Main(string[] args)
{
    for(var i=1; i<=100; i++)
    {
        var word = FizzBuzz(i);
        Console.Write($"{word} ");
    }
}

It wasn't until I wrote this in C that I realised how wasteful this approach is. Memory management in C is handled manually, so it was immediately obvious what the issue was. In the C# code we create a string for each call to FizzBuzz. This happens in a loop, so we rapidly allocate several strings. However each one is only used once in the loop. After that we have to wait for the garbage collector to notice this and reclaim the memory used by the string.

In C I decided to pass a buffer into the function instead. Each time through the loop we clear the buffer, write to it, then print it out. There is more work expected of the caller, but we are much more effecient in our usage of memory.


void fizzBuzz(int num, char *buf)
{
    bool isFizz = num % 3 == 0;
    bool isBuzz = num % 5 == 0;

    if (isFizz && isBuzz)
    {
        sprintf(buf, "%s", "FizzBuzz");
    }
    else if(isFizz)
    {
        sprintf(buf, "%s", "Fizz");
    }
    else if(isBuzz)
    {
        sprintf(buf, "%s", "Buzz");
    }
    else
    {
        sprintf(buf, "%d", num);
    }
}

int main()
{
    const size_t BUF_MAX = 128;
    char *buf = (char *)malloc(sizeof(char) * BUF_MAX);

    for (int i=1; i<=100; i++)
    {
        memset(buf, '\0', BUF_MAX);
        fizzBuzz(i, buf);
        printf("%s ", buf);
    }

    free(buf);
    buf = NULL;

    return 0;
}

Taking time to write even simple things in other languages can change our perspective.

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