How do i write a program
in C to do split and merge
operation. I have configured
my system with opencv.

You forgot to mention you are a C beginner like in your other 4 threads.

I would advise you not take on such complicated projects as a beginner.

If you choose to do so anyway, then it's best to post the code you have tried.

this is the code that i tried.

#include <opencv2/highgui/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <iostream>

using namespace cv;
using namespace std;

Mat img;
Size size;

struct region {
    // tree data structure
    vector<region> childs;
    bool validity; // TODO: have a method for clear the data structure and remove regions with false validity

    // tree for split&merge procedure
    Rect roi;
    Mat m;
    Scalar label;
    Mat mask; // for debug. don't use in real cases because it is computationally too heavy.
};

//---------------------------------------------------------------------------------------------------------------

-------- merging
bool mergeTwoRegion(region& parent, const Mat& src, region& r1, region& r2,  bool (*predicate)(const Mat&)) {
    if(r1.childs.size()==0 && r2.childs.size()==0) {

        Rect roi1 = r1.roi;
        Rect roi2 = r2.roi;
        Rect roi12 = roi1 | roi2;
        if(predicate( src(roi12) )) {
            r1.roi = roi12;

            // recompute mask
            r1.mask = Mat::zeros(size, CV_8U);
            rectangle(r1.mask, r1.roi, 1, CV_FILLED);

            r2.validity = false;
            return true;
        }
    }
    return false;
}

void merge(const Mat& src, region& r, bool (*predicate)(const Mat&)) {
    // check for adjiacent regions. if predicate is true, then  merge.
    // the problem is to check for adjiacent regions.. one way can be:
    // check merging for rows. if neither rows can be merged.. check for cols.

    bool row1=false, row2=false, col1=false, col2=false;

    if(r.childs.size()<1) return;

    // try with the row
    row1 = mergeTwoRegion(r, src, r.childs[0], r.childs[1], predicate);
    row2 = mergeTwoRegion(r, src, r.childs[2], r.childs[3], predicate);

    if( !(row1 | row2) ) {
        // try with column
        col1 = mergeTwoRegion(r, src, r.childs[0], r.childs[2], predicate);
        col2 = mergeTwoRegion(r, src, r.childs[1], r.childs[3], predicate);
    } 

    for(int i=0; i<r.childs.size(); i++) {
        if(r.childs[i].childs.size()>0) 
            merge(src, r.childs[i], predicate);
    }
}

//---------------------------------------------------------------------------------------------------------------

-------- quadtree splitting
region split(const Mat& src, Rect roi, bool (*predicate)(const Mat&)) {
    vector<region> childs;
    region r;

    r.roi = roi;
    r.m = src;
    r.mask = Mat::zeros(size, CV_8U);
    rectangle(r.mask, r.roi, 1, CV_FILLED);
    r.validity = true;

    bool b = predicate(src);
    if(b) {
        Scalar mean, s;
        meanStdDev(src, mean, s);
        r.label = mean;
    } else {
        int w = src.cols/2;
        int h = src.rows/2;
        region r1 = split(src(Rect(0,0, w,h)), Rect(roi.x, roi.y, w,h), predicate);
        region r2 = split(src(Rect(w,0, w,h)), Rect(roi.x+w, roi.y, w,h), predicate);
        region r3 = split(src(Rect(0,h, w,h)), Rect(roi.x, roi.y+h, w,h), predicate);
        region r4 = split(src(Rect(w,h, w,h)), Rect(roi.x+w, roi.y+h, w,h), predicate);
        r.childs.push_back( r1 );
        r.childs.push_back( r2 );
        r.childs.push_back( r3 );
        r.childs.push_back( r4 );
    }
    //merge(img, r, predicate);
    return r;
}

//---------------------------------------------------------------------------------------------------------------

-------- tree traversing utility
void print_region(region r) {
    if(r.validity==true && r.childs.size()==0) {
        cout << r.mask << " at " << r.roi.x << "-" << r.roi.y << endl;
        cout << r.childs.size() << endl;
        cout << "---" << endl;
    }
    for(int i=0; i<r.childs.size(); i++) {
        print_region(r.childs[i]);
    }
}

void draw_rect(Mat& imgRect, region r) {
    if(r.validity==true && r.childs.size()==0) 
        rectangle(imgRect, r.roi, 50, .1);
    for(int i=0; i<r.childs.size(); i++) {
        draw_rect(imgRect, r.childs[i]);
    }
}

void draw_region(Mat& img, region r) {
    if(r.validity==true && r.childs.size()==0) 
        rectangle(img, r.roi, r.label, CV_FILLED);
    for(int i=0; i<r.childs.size(); i++) {
        draw_region(img, r.childs[i]);
    }
}

//---------------------------------------------------------------------------------------------------------------

-------- split&merge test predicates
bool predicateStdZero(const Mat& src) {
    Scalar stddev, mean;
    meanStdDev(src, mean, stddev);
    return stddev[0]==0;
}
bool predicateStd5(const Mat& src) {
    Scalar stddev, mean;
    meanStdDev(src, mean, stddev);
    return (stddev[0]<=5.8) || (src.rows*src.cols<=25);
}

//---------------------------------------------------------------------------------------------------------------

-------- main
int main( int /*argc*/, char** /*argv*/ )
{
    img = (Mat_<uchar>(4,4) << 0,0,1,1,
                               1,1,1,1, 
                               3,3,3,3,
                               3,4,4,3);

    cout << img << endl;
    size = img.size();

    region r;
    r = split(img, Rect(0,0,img.cols,img.rows), &predicateStdZero);
    merge(img, r, &predicateStdZero);
    cout << "------- print" << endl;
    print_region(r);

    cout << "-----------------------" << endl;

    img = imread("lena.jpg", 0);

    // round (down) to the nearest power of 2 .. quadtree dimension is a pow of 2.
    int exponent = log(min(img.cols, img.rows)) / log (2);
    int s = pow(2.0, (double)exponent);
    Rect square = Rect(0,0, s,s);
    img = img(square).clone();

    namedWindow("original", CV_WINDOW_AUTOSIZE);
    imshow( "original", img );

    cout << "now try to split.." << endl;
    r = split(img, Rect(0,0,img.cols,img.rows), predicateStd5);

    cout << "splitted" << endl;
    Mat imgRect = img.clone();
    draw_rect(imgRect, r);
    namedWindow("split", CV_WINDOW_AUTOSIZE);
    imshow( "split", imgRect );
    imwrite("split.jpg", imgRect);

    merge(img, r, &predicateStd5);
    Mat imgMerge = img.clone();
    draw_rect(imgMerge, r);
    namedWindow("merge", CV_WINDOW_AUTOSIZE);
    imshow( "merge", imgMerge );
    imwrite( "merge.jpg", imgMerge );

    Mat imgSegmented = img.clone();
    draw_region(imgSegmented, r);
    namedWindow("segmented", CV_WINDOW_AUTOSIZE);
    imshow( "segmented", imgSegmented );
    imwrite( "segmented.jpg", imgSegmented );

    while( true )
    {
        char c = (char)waitKey(10);
        if( c == 27 ) { break; }
    }

    return 0;
}

Not bad for a beginner.
If you can just describe what is wrong with your code, someone might be better able to help.

Any errors you are receiving etc...