Python: I fell in an infinite loop

Question

The problem states as follows:

Example output:

Calculator
Give the first number: 100
Give the second number: 25
(1) +
(2) -
(3) *
(4) /
(5)Change numbers
(6)Quit
Current numbers: 100 25
Please select something (1-6): 5
Give the first number: 10
Give the second number: 30
(1) +
(2) -
(3) *
(4) /
(5)Change numbers
(6)Quit
Current numbers: 10 30
Please select something (1-6): 1
The result is: 40
(1) +
(2) -
(3) *
(4) /
(5)Change numbers
(6)Quit
Current numbers: 10 30
Please select something (1-6): 6
Thank you!

And my solution was:

print("Calculator")

var1 = input("Give the first number: ")
var2 = input("Give the second number: ")

print("(1) +\n(2) -\n(3) *\n(4) /\n(5)Change numbers\n(6)Quit")
print("Current numbers: " + var1 + " " + var2)

opcion = input("Please select something (1-6): ")

while (opcion != "6"):
    if (opcion == "1"):
        var3 = int(var1) + int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "2"):
        var3 = int(var1) - int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "3"):
        var3 = int(var1) * int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "4"):
        var3 = int(var1) / int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "5"):
        var1 = input("Give the first number: ")
        var2 = input("Give the second number: ")
        opcion = input("Please select something (1-6): ")
    else:
        print("Selection was not correct.")

print("Thank you!")

But in "elif (opcion == "5"):" the automatic corrector states that I fell in an infinite loop, I tried a break after the two new numbers are entered, but it completely exits from the while-loop, any ideas? Thank you.

Answer 1

Problem in your code:

You only assign opcion outside the while loop and after which you are only modifying opcion when opcion == "5".

What happens when you give opcion = "1" is it adds and gives you the answer and after which checks the while statement when is true, because opcion did not change. It then adds again, and checks again, and goes oooooooooooon, so an infinite loop is produced.

Modification:

print("Calculator")

var1 = input("Give the first number: ")
var2 = input("Give the second number: ")

print("(1) +\n(2) -\n(3) *\n(4) /\n(5)Change numbers\n(6)Quit")
print("Current numbers: " + var1 + " " + var2)

while True:
    opcion = input("Please select something (1-6): ")
    if (opcion == "1"):
        var3 = int(var1) + int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "2"):
        var3 = int(var1) - int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "3"):
        var3 = int(var1) * int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "4"):
        var3 = int(var1) / int(var2)
        print("The result is: " + str(var3))
    elif (opcion == "5"):
        var1 = input("Give the first number: ")
        var2 = input("Give the second number: ")
    elif (opcion == "6"):
        break
    else:
        print("Selection was not correct.")

print("Thank you!")

More improved solution:

import operator
print("Calculator")

var1 = input("Give the first number: ")
var2 = input("Give the second number: ")

print("(1) +\n(2) -\n(3) *\n(4) /\n(5)Change numbers\n(6)Quit")
print("Current numbers: " + var1 + " " + var2)
operations={"1":operator.add,"2":operator.sub,"3":operator.mul,"4":operator.div}
while True:
    option = input("Please select something (1-6): ")
    print option
    if option in operations:
        var3=operations[option](int(var1),int(var2))        
        print "value"+str( var3)
        continue
    if (option == "6"):
        print "quiting"
        break
    elif (option == "5"):
        var1 = input("Give the first number: ")
        var2 = input("Give the second number: ")
    else:
        print("Selection was not correct.")

print("Thank you!")

Note :

It should be options and not opcion in correct English terms but it really doesn't matter :P