Why my for loop is not iterating to the rows in 2D array ?

#include <iostream>
using namespace std;

//row-wise binary search.

int search2DArray(int matrix[][4], int n, int m, int key){
int start = 0, end = m-1;

for(int i=0; i<n; i++){

    while(start<=end){
        int mid = (start+end)/2;

        if(matrix[i][mid] == key){
            cout<<"FOUNDn";
            return 0;
        }else if(matrix[i][mid] < key){ 
            start = mid + 1;
        }else{
            end = mid - 1;
        }   
    }

}
cout<<"NOT FOUNDn";
return -1;

}

int main(){

int matrix[4][4] = {{10,20,30,40},
                    {15,25,35,45},
                    {27,29,37,48},
                    {32,33,39,50}};

search2DArray(matrix, 4, 4, 29);

return 0;

}

I tried to apply for loop to iterate all the rows of 2D array but couldn’t get past the first row and always printing NOT FOUND for any input for row > 0.