i created a code that solves mathematic problems by the user. The problems have to involve addition, subtraction, division or multiplication. the code runs without any errors but the issue is I want the code to give two distinct messages for the user.

1. when the user runs the code for the first time "Please enter the problem in this format (number1 operator number2) or type 'stop' to exist"
2. when the user enters the problem in the wrong format "invalid enter please try again with the right format or enter 'stop' to exist'

while True:
    while True:
        problem = input("Please enter the problem in this format (number1 operator number2) or type 'stop' to exist: ").split()
        if problem[0] == 'stop':
            break
        if len(problem) != 3:
            continue
        n1,op,n2 = problem
        if any( not (n.isnumeric() or n.count('.')==1 and n.replace('.','').isnumeric()) for n in (n1,n2) ):
            continue
        if op not in (' ','-','*','/','//','**'):
        #this is the tuple of operators which tell the computer which operature the user is using
            continue
        break
    if problem[0] == 'stop':
        break
    match op:
        case ' ': result = float(n1) float(n2)
        case '-': result = float(n1)-float(n2)
        case '*': result = float(n1)*float(n2)
        case '**': result = float(n1)**float(n2)
        case '/': result = float(n1)/float(n2)
            #this will give a float answer. Ex: 1 / 9 = 0.11
        case '//': result = float(n1)//float(n2)
            #this will give an integer answer. Ex: 1 / 9 = 0
    print(f'{result:,.2f}')
    

CodePudding user response：

an improved version of your code

print("Please enter the problem in this format (number1 operator number2) or type 'stop' to exist: ")
while True:
    problem = input("").split()
    operators = [' ','-','*','/','//','**']

    if problem[0] == 'stop':
        break
    if len(problem) != 3:
        print('invalid entry please try again with the right format or enter stop to exist')
    else:
        if (problem[0].isdigit() == True) and(problem[1] in operators) and (problem[2].isdigit() == True):

            n1 = float(problem[0])
            n2 = float(problem[2])

            if problem[1] == ' ':
                result = n1   n2
            elif problem[1] == '-':
                result = n1 - n2
            elif problem[1] == '*':
                result =  n1 * n2
            elif problem[1] == '**':
                result = n1**n2
            elif problem[1] == '/':
                result = n1/n2
            elif problem[1] == '//':
                result = n1//n2

            print('\n', result, '\n')
        else:
            print('invalid entry please try again with the right format or enter stop to exist')

Output

Please enter the problem in this format (number1 operator number2) or type 'stop' to exist: 
4

invalid entry please try again with the right format or enter stop to exist
4   1

5.0 

stop #exit the program

CodePudding user response：

import sys


def main():
    operators = [' ', '-', '/', '*', '**']
    while True:

        while True:
            user_input = input("Please enter the problem in this format (num operator num) or type 'stop' to quite:\n> ").split()
            if ''.join(user_input) == 'stop':
                print('Goodbye!')
                sys.exit()
            else:
                n1, operator, n2 = user_input[0], user_input[1], user_input[2]
                if len(user_input) != 3:
                    print('not enough input', user_input)
                elif not n1.isdigit() and not n2.isdigit():
                    print(f'{n1} or {n2} was not a valid digit')
                elif operator not in operators:
                    print(f'{operator} was an invalid operator')
                    continue
                else:
                    break
       
        result = ''.join((n1, operator, n2))
        print(f'You entered {n1} {operator} {n2} = {eval(result)}')


if __name__ == '__main__':
    main()