# Simple calculator program using Python3

In this post we are going to learn how to use Python’s while loop, if conditioning, break, taking input from user.

Well that seems a lot, but its all simple when you look at the program.

```#subroutine to calculate addition and subtraction by taking user choice as input
def operate(o):
#convert user input into integer
a = int(input("enter first number "))
b = int(input("enter second number "))
if(o == "a"):
return a+b
elif(o == "s"):
return a-b
#execution starts from here
operation = input("Enter your choice: ")
total = 0
while(operation!=""):
if(operation == "a"):
total = operate(operation)
elif(operation == "s"):
print("you choose substraction")
total = operate(operation)
else:
print("you choose nothing")
#print the actual result
print("Result = ",total)
#choice of user which decided whether to continue or not
choice = input("Do you want to continue?Type Y to continue or any other key to quit: ")
if(choice == "y"):
operation = input("Enter your choice: ")
else:
break```

For easier understanding let me explain it to you in the form of algorithm.

• Execution starts from asking user the input.
• Then using if condition we check what type of operation the user has chosen.
• Then according to the operation we call the subroutine and result is returned.
• At the end we ask the user once more if the user wants to continue or exit.

If any doubts or needed clarifications don’t forget to comment.