Get to know opencv4.x for the first time --- add salt and pepper noise to the image

// Add salt and pepper noise to the image 
#include <stdio.h>
#include <iostream>
#include <string>
#include <opencv2\opencv.hpp>
using namespace std;
using namespace cv;
void add_salt(Mat & img);
int main()
{
    
	// Salt and pepper noise , As the name suggests, it is to sprinkle white salt and black pepper on the image 
	Mat img = imread("person3.jpeg");// Read the three channel image 
	namedWindow(" Original picture ", WINDOW_NORMAL);
	imshow(" Original picture ", img);
	for (int i = 0; i < img.cols*img.rows / 10; i++)
	{
    
		add_salt(img);
	}
	namedWindow(" Salt and pepper map ", WINDOW_NORMAL);
	imshow(" Salt and pepper map ", img);
	waitKey(0);
	return 0;
}
void add_salt(Mat & img)
{
    
	int x = std::rand() % img.cols;// Get the column position where the noise is increased 
	int y = std::rand() % img.rows;// Get the row position where the noise is increased 
	int select = std::rand() % 100;// And 50 Comparison is used to decide whether to sprinkle salt or pepper 
	if (img.channels() == 3)
	{
    
		if (select >= 50)// Sprinkle salt 
		{
    
			img.at<Vec3b>(y, x)[0] = 255;
			img.at<Vec3b>(y, x)[1] = 255;
			img.at<Vec3b>(y, x)[2] = 255;
		}
		else// Sprinkle black pepper 
		{
    
			img.at<Vec3b>(y, x)[0] = 0;
			img.at<Vec3b>(y, x)[1] = 0;
			img.at<Vec3b>(y, x)[2] = 0;
		}
	}
	else// grayscale 
	{
    
		if (select >= 50)// Sprinkle salt 
		{
    
			img.at<float>(y, x) = 255;
		}
		else// Sprinkle black pepper 
		{
    
			img.at<float>(y, x) = 0;
		}
	}
}