For example, consider the following code. It is a function that outputs a histogram of an image.

int histgram(unsigned char image[HEIGHT][WIDTH][3], int hist[256])
{
    for (int i = 0; i < 256; i++)
    {
        hist[i] = 0;
    }

    for (int i = 0; i < HEIGHT; i++)
    {
        for (int j = 0; j < WIDTH; j++)
        {
            hist[image[i][j][1]]++;
        }
    }
    return 0;
}

int main(int argc, char** argv)
{
    if (argc != 4)
    {
        fprintf(stderr, "<input.ppm> <output.csv> <output.ppm>");
        exit(1);
    }

    unsigned char image[HEIGHT][WIDTH][3];

    loadImage(image, argv[1]);

    int hist[256];
    histgram(image, hist);
    saveImage(image, argv[3]);

    return 0;
}

If you initialize the array once and then use the { 0 } syntax when editing its values, like:

int hist[N};
hist = { 0 };

you’ll get no outputs (I have already confirmed this). However, initialization with 0 is possible by declaring:

int hist[N] = { 0 };

What exactly is {0}? Why doesn’t a code that assigns {0} after initialization fail?

Why can’t { 0 } be used to set all already declared arrays together to 0? Why not use such a language specification?