# Calculator Program in Python

Python programming is a great tool to evaluate and make manipulations. In this article, We will be learning a simple command-line calculator program in Python 3.

We’ll be using mathematical operators, Conditional statements, functions and handle user input to make our calculator.

## Prerequisites

The system should have Python 3 installed on the local computer and have a programming environment set up on the machine.

## Accept/Prompt Input from User

We’ll be accepting input from the user. To serve this purpose, we will be using the input() function of Python. For this program, we will let the user input two numbers, so let’s have the program for prompt of the two numbers.

```num_1 = input('Enter your first number: ')
num_2 = input('Enter your second number: ')
```

Output:

```Enter your first number: 10
```

We should save the program before we run it. You should be able to type into the terminal window in response to each prompt.

## Defining and using Operators

Now, let’s add the operators such as addition, multiplication, division and subtraction to our Calculator program.

```num_1 = int(input('Enter your first number: '))
num_2 = int(input('Enter your second number: '))

print('{} + {} = '.format(num_1, num_2))
print(num_1 + num_2)

# Subtraction
print('{} - {} = '.format(num_1, num_2))
print(num_1 - num_2)

# Multiplication
print('{} * {} = '.format(num_1, num_2))
print(num_1 * num_2)

# Division
print('{} / {} = '.format(num_1, num_2))
print(num_1 / num_2)
# The format() will help out output look descent and formatted.
```

Output:

```Enter your first number: 15
15 + 10 =
25
15 - 10 =
05
15 * 10 =
150
15 / 10 =
1.5
```

If you have a look at the above output, we can notice that as soon as the user enters `num_1` as `15` and `num_2` as `10`, all the operations of the calculator gets executed.

If we want to limit the program to only perform one operation at a time, we’ll have to use conditional statements and make the entire calculator program to be user’s choice based operation program.

## Including condition statement to make the program as User’s choice

So, we will start by adding some information at the top of the program, along with a choice to make, in order to make the user understand what he/she is supposed to choose.

```choice = input('''
Please select the type of operation you want to perform:
- for subtraction
* for multiplication
/ for division
''')

num_1 = int(input('Enter your first number: '))
num_2 = int(input('Enter your second number: '))

if choice == '+':
print('{} + {} = '.format(num_1, num_2))
print(num_1 + num_2)

elif choice == '-':
print('{} - {} = '.format(num_1, num_2))
print(num_1 - num_2)

elif choice == '*':
print('{} * {} = '.format(num_1, num_2))
print(num_1 * num_2)

elif choice == '/':
print('{} / {} = '.format(num_1, num_2))
print(num_1 / num_2)

else:
print('Enter a valid operator, please run the program again.')
```

Output:

```Please select the type of operation you want to perform: