OpenCV Image Filtering

// Reference : http://docs.opencv.org/3.0.0/dc/dd3/tutorial_gausian_median_blur_bilateral_filter.html
// Examples : Smoothing Images
 
#include <iostream>
#include <cv.hpp>
#include <windows.h>
 
using namespace std;
using namespace cv;
 
int DELAY_CAPTION = 1500;
int DELAY_BLUR = 100;
int MAX_KERNEL_LENGTH = 31;
 
int display_caption(char *caption);
int display_dst(int delay);
char window_name[] = "Filter Demo 1";
 
Mat src, dst;
 
int main()
{
    namedWindow(window_name);
    
    Sleep(2000);
 
    src = imread("img/lena.bmp");
 
    if (display_caption("Original Image") != 0)
        return 0;
 
    dst = src.clone();
    if (display_dst(DELAY_CAPTION) != 0)
        return 0;
    
    
    for (int i = 1; i < MAX_KERNEL_LENGTH; i = i + 2)
    {
        blur(src, dst, Size(i, i), Point(-1, -1));
        if (display_dst(DELAY_BLUR) != 0)
            return 0;
 
        if (display_caption("Gaussian Blur") != 0)
            return 0;
 
        for (int i = 1; i < MAX_KERNEL_LENGTH; i = i + 2)
        {
            GaussianBlur(src, dst, Size(i, i), 0, 0);
            if (display_dst(DELAY_BLUR) != 0)
                return 0;
        }
 
        if (display_caption("Median Blur") != 0)
            return 0;
 
        for (int i = 1; i < MAX_KERNEL_LENGTH; i = i + 2)
        {
            medianBlur(src, dst, i);
            if (display_dst(DELAY_BLUR) != 0)
                return 0;
        }
 
        if (display_caption("Bilateral Blur") != 0)
            return 0;
        
        for (int i = 1; i < MAX_KERNEL_LENGTH; i = i + 2)
        {
            bilateralFilter(src, dst, i, i * 2, i / 2);
            if (display_dst(DELAY_BLUR) != 0)
                return 0;
        }
 
        display_caption("End");
 
        waitKey(0);
        return 0;
    }
}
 
int display_caption(char *caption)
{
    dst = Mat::zeros(src.size(), src.type());
    putText(dst, caption, Point(src.cols / 4, src.rows / 2), FONT_HERSHEY_COMPLEX, 1, Scalar(255, 255, 255));
 
    imshow(window_name, dst);
    int c = waitKey(DELAY_CAPTION);
    if (c >= 0)
        return -1;
    
    return 0;
}
 
int display_dst(int delay)
{
    imshow(window_name, dst);
    int c = waitKey(delay);
    if (c >= 0)
        return -1;
    
    return 0;
}