My heuristic in Parts B and C is 10 points for each 3-in-a-row found in the game board, and 3 points for each 2-in-a-row. Points are positive for MAX and negative for MIN. A win for MAX is +100000 and a win for MIN is -100000. Note that this heuristic doesn't even look for open spaces on the ends of the 3-in-a-rows or 2-in-a-rows, so it will make dumb moves every so often.
Here is an example of how the program for Part B might look. I include a lot of diagnostic messages (such as the minimax value and best moves) which you do not have to report, but are useful for testing.
Enter rows: 6 Enter columns: 7 Enter n-in-a-row: 4 Enter cutoff depth: 5 Playing game with rows=6, cols=7, and n-in-a-row=4 Beginning game. It is the computer's turn (MAX). ....... ....... ....... ....... ....... ....... Minimax calculation completed in 19.19 ms Transposition table has 885 states. The minimax value for this state is 13 The best column to move in is 0 The computer picks 0 It is the user's turn (MIN). ....... ....... ....... ....... ....... X...... Minimax calculation completed in 1.612 ms Transposition table has 237 states. The minimax value for this state is 0 The best column to move in is 0 What column to move in? 3 It is the computer's turn (MAX). ....... ....... ....... ....... ....... X..O... Minimax calculation completed in 8.102 ms Transposition table has 769 states. The minimax value for this state is 16 The best column to move in is 0 The computer picks 0 It is the user's turn (MIN). ....... ....... ....... ....... X...... X..O... Minimax calculation completed in 1.144 ms Transposition table has 284 states. The minimax value for this state is 3 The best column to move in is 0 What column to move in? 4 It is the computer's turn (MAX). ....... ....... ....... ....... X...... X..OO.. Minimax calculation completed in 1.804 ms Transposition table has 233 states. The minimax value for this state is 43 The best column to move in is 0 The computer picks 0 It is the user's turn (MIN). ....... ....... ....... X...... X...... X..OO.. Minimax calculation completed in 3.170 ms Transposition table has 567 states. The minimax value for this state is -3 The best column to move in is 0 What column to move in? 0 It is the computer's turn (MAX). ....... ....... O...... X...... X...... X..OO.. Minimax calculation completed in 9.704 ms Transposition table has 1250 states. The minimax value for this state is 23 The best column to move in is 5 The computer picks 5 It is the user's turn (MIN). ....... ....... O...... X...... X...... X..OOX. Minimax calculation completed in 5.822 ms Transposition table has 1303 states. The minimax value for this state is -26 The best column to move in is 3 What column to move in? 4 It is the computer's turn (MAX). ....... ....... O...... X...... X...O.. X..OOX. Minimax calculation completed in 9.795 ms Transposition table has 1659 states. The minimax value for this state is 0 The best column to move in is 1 The computer picks 1 It is the user's turn (MIN). ....... ....... O...... X...... X...O.. XX.OOX. Minimax calculation completed in 5.155 ms Transposition table has 1547 states. The minimax value for this state is -33 The best column to move in is 3 What column to move in? 5 It is the computer's turn (MAX). ....... ....... O...... X...... X...OO. XX.OOX. Minimax calculation completed in 9.189 ms Transposition table has 1273 states. The minimax value for this state is 7 The best column to move in is 4 The computer picks 4 It is the user's turn (MIN). ....... ....... O...... X...X.. X...OO. XX.OOX. Minimax calculation completed in 3.521 ms Transposition table has 1181 states. The minimax value for this state is -43 The best column to move in is 3 What column to move in? 5 It is the computer's turn (MAX). ....... ....... O...... X...XO. X...OO. XX.OOX. Minimax calculation completed in 6.589 ms Transposition table has 1509 states. The minimax value for this state is -10 The best column to move in is 1 The computer picks 1 It is the user's turn (MIN). ....... ....... O...... X...XO. XX..OO. XX.OOX. Minimax calculation completed in 8.372 ms Transposition table has 1288 states. The minimax value for this state is -40 The best column to move in is 5 What column to move in? 6 It is the computer's turn (MAX). ....... ....... O...... X...XO. XX..OO. XX.OOXO Minimax calculation completed in 4.684 ms Transposition table has 930 states. The minimax value for this state is 73 The best column to move in is 1 The computer picks 1 It is the user's turn (MIN). ....... ....... O...... XX..XO. XX..OO. XX.OOXO Minimax calculation completed in 2.217 ms Transposition table has 594 states. The minimax value for this state is 0 The best column to move in is 1 What column to move in? 1 It is the computer's turn (MAX). ....... ....... OO..... XX..XO. XX..OO. XX.OOXO Minimax calculation completed in 5.288 ms Transposition table has 1357 states. The minimax value for this state is 43 The best column to move in is 3 The computer picks 3 It is the user's turn (MIN). ....... ....... OO..... XX..XO. XX.XOO. XX.OOXO Minimax calculation completed in 3.744 ms Transposition table has 1146 states. The minimax value for this state is 20 The best column to move in is 5 What column to move in? 6 It is the computer's turn (MAX). ....... ....... OO..... XX..XO. XX.XOOO XX.OOXO Minimax calculation completed in 9.218 ms Transposition table has 760 states. The minimax value for this state is 47619 The best column to move in is 2 The computer picks 2 It is the user's turn (MIN). ....... ....... OO..... XX..XO. XX.XOOO XXXOOXO Minimax calculation completed in 2.083 ms Transposition table has 632 states. The minimax value for this state is 47619 The best column to move in is 0 What column to move in? 5 It is the computer's turn (MAX). ....... ....... OO...O. XX..XO. XX.XOOO XXXOOXO Minimax calculation completed in 2.159 ms Transposition table has 450 states. The minimax value for this state is 47619 The best column to move in is 2 The computer picks 2 Winner is MAX: ....... ....... OO...O. XX..XO. XXXXOOO XXXOOXO