Template with Vector and stb_image

#define _CRT_SECURE_NO_WARNINGS 1
#include <vector>

#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

static inline double sqr(double x) { return x * x; }

class Vector {
public:
    explicit Vector(double x = 0, double y = 0, double z = 0) {
        coord[0] = x;
        coord[1] = y;
        coord[2] = z;
    }
    double& operator[](int i) { return coord[i]; }
    double operator[](int i) const { return coord[i]; }

    Vector& operator+=(const Vector& v) {
        coord[0] += v[0];
        coord[1] += v[1];
        coord[2] += v[2];
        return *this;
    }

    double norm2() const {
        return sqr(coord[0]) + sqr(coord[1]) + sqr(coord[2]);
    }

    double coord[3];
};

Vector operator+(const Vector& a, const Vector& b) {
    return Vector(a[0] + b[0], a[1] + b[1], a[2] + b[2]);
}
Vector operator-(const Vector& a, const Vector& b) {
    return Vector(a[0] - b[0], a[1] - b[1], a[2] - b[2]);
}
Vector operator*(const Vector& a, double b) {
    return Vector(a[0]*b, a[1]*b, a[2]*b);
}
Vector operator*(double a, const Vector& b) {
    return Vector(a*b[0], a*b[1], a*b[2]);
}

double dot(const Vector& a, const Vector& b) {
    return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
}


int main() {
    int W = 512;
    int H = 512;

    Vector center(0.2, 0.1, 0.);

    std::vector<unsigned char> image(W*H * 3, 0);
#pragma omp parallel for
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {

            Vector v(j / (double)W - 0.5, i / (double)H - 0.5, 0.);
            double gaussianVal = exp(-(v-center).norm2()/(2*sqr(0.2)));

            image[(i*W + j) * 3 + 0] = 127* gaussianVal;   // RED
            image[(i*W + j) * 3 + 1] = 50 * gaussianVal;  // GREEN
            image[(i*W + j) * 3 + 2] = 255 * gaussianVal;  // BLUE
        }
    }
    stbi_write_png("image.png", W, H, 3, &image[0], 0);

    return 0;
}