#
# ps11pr2.py (Problem Set 11, Problem 2)
# Fall 2021
# Matrix operations
#
# 

def display_menu():
    """ prints a menu of options
    """  
    print()
    print('(0) Enter a new matrix')
    print('(1) Negate the matrix')
    print('(2) Multiply a row by a constant')
    print('(3) Add one row to another')
    print('(4) Add a multiple of one row to another')
    print('(5) Transpose the matrix')
    print('(6) Quit')
    print()

def print_matrix(matrix):
    """ prints the specified matrix in rectangular form.
        input: matrix is a 2-D list numbers
    """
    ## You will revise this function. 
    print(matrix)
       
def get_matrix():
    """ gets a new matrix from the user and returns it
    """
    matrix = eval(input('Enter a new 2-D list of numbers: '))
    return matrix

def negate_matrix(matrix):
    """ negates all of the elements in the specified matrix
        inputs: matrix is a rectangular 2-D list of numbers
    """
    for r in range(len(matrix)):
        for c in range(len(matrix[0])):
            matrix[r][c] *= -1
    # We don't need to return the matrix!
    # All changes to the matrix will still be there when the
    # function returns, because we received a copy of the
    # *reference* to the matrix used by main().

### Add your functions for options 2-5 here. ###

def main():
    """ the main user-interaction loop
    """
    ## The default starting matrix.
    ## DO NOT CHANGE THESE LINES.
    matrix = [[ 1,  2,  3,  4],
              [ 5,  6,  7,  8],
              [ 9, 10, 11, 12]]

    while True:
        print()
        print_matrix(matrix)
        display_menu()
        choice = int(input('Enter your choice: '))

        if choice == 0:
            matrix = get_matrix()
        elif choice == 1:
            negate_matrix(matrix)

        ## add code to handle the other options here

        elif choice == 6:
            break
        else:
            print('Invalid choice. Try again.')