How to Create a Simple Calculator in Python

Submitted by Yorkiebar on Saturday, March 15, 2014 - 10:35.
Introduction: This tutorial is on how to create a simple calculator in Python. The Theory: Here's how the program will be structured: Get the users first number Get the users second number Get the users action Use if statements to perform the calculation Print out the result Getting The Users Numbers: First we want to get the users two numbers to calculate together somehow. We use input statements to allow the user to enter a string, we use an int cast around the input statement to convert their string input to a integer for us to use in our calculations...
  1. num1 = int(input("Enter your first number: "));
  2. num2 = int(input("Enter your second number: "));
This is good but the user could enter an invalid number, so lets add some exception handling...
  1. pass1 = -1;
  2. while (pass1 < 0):
  3.     try:
  4.         num1 = int(input("Enter your first number: "));
  5.         pass1 = 10;
  6.     except ValueError:
  7.         pass1 = -1;
  8.         print("That is not a valid number. It must be a whole number...");
  9. pass2 = -1;
  10. while (pass2 < 0):
  11.     try:
  12.         num2 = int(input("Enter your second number: "));
  13.         pass2 = 10;
  14.     except ValueError:
  15.         pass2 = -1;
  16.         print("That is not a valid number. It must be a whole number...");
So now the script creates two variables "pass1" and "pass" and sets them both to minus 1 (-1). Then, while the relevant pass variable is below 0, it asks for a nuumber. If no exception is thrown, the pass variable is set higher than 0 and the loop is passed, otherwise an error statement is printed and pass1 is re-set back below zero (this isn't necessary but it makes it simpler to understand). Asking For The Action: Next we want the action for the two numbers, this is similar to before...
  1. pass3 = -1;
  2. while (pass3 < 0):
  3.     try:
  4.         action = input("Enter your action (+/*-): ");
  5.         if (action == "+" or action == "-" or action == "/" or action == "*"):
  6.             pass3 = 10;
  7.     except:
  8.         pass3 = -1;
  9.         print("That is not a valid action. It must be +, -, /, or *...");
Validating The Action and Performing The Calculation: Finally we want to perform the calculation depending on what the action entered by the user was...
  1. if (action == "+"):
  2.     end = num1 + num2;
  3. elif (action == "-"):
  4.     end = num1 - num2;
  5. elif (action == "/"):
  6.     end = num1 / num2;
  7. elif (action == "*"):
  8.     end = num1 * num2;
  9. else:
  10.     print("Error...");
Last but not least, we output the result...
  1. print("Your result is: " + str(end))
Tags
Calculator
Python

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