// M[][] is the matrix which stores everything.
// Let 1st player be 1 and 2nd player be -1
// Initialize the matrix with all 0
int number_of_column = 6;
int number_of_rows = 7;

// Check for sinking effect when something is added (I have not added the boundary conditions try that)
// Add checks for invalid selection.
// The position to add the piece was give 2,3
int i = 2;
for(; i < number_of_rows && M[i][3] != 0; i++)
// The loop will stop with i containing the value of first non-zero element (non free spot, we have to insert it one element above)
M[i-1][3] = 1   // For 1st player. // Remember to check for edge cases here and invalid options its important.

// Check horizontal connect 4 (Try to implement vertical in a similar manner)
// Say the user just added 1 to M[a][b]
// Check the left side of the piece (include the piece)
int count = 0;  // Stores how many continous same player pieces we saw.
for(int i = b; i > 0 && M[a][i] == M[a][b]; i--) {
    count ++;
}
// Check the right side but do not include the piece.
for(int i = b+1; i < number_of_column && M[a][i] == M[a][b]; i++) {
    count ++;
}
// Check if we say 4 pieces of the same type
if(count >= 4) {
    // 1st user wins.
}

// Diagonal check.
// 2 cases, 45 degree diagonal and 135 degree diagonal.
// I will show you 45, you can implement 135.
// Check the right-up direction including the piece.
// Piece was added to M[a][b]
int count = 0;
for(int i=a, j=b; i >= 0 && j < number_of_column && M[i][j] == M[a][b]; i--, j++) {
    count ++;
}
// Check the left-bottom direction not including the piece.
for(int i=a+1, j=b-1; i < number_of_rows && j > 0 && M[i][j] == M[a][b]; i++, j--) {
    count ++;
}
// Check if we have connect 4 same like above.
if(count >= 4) {
    // 1st user wins.
}