In this example you will learn to create a simple calculator that can add, subtract, multiply or divide depending upon the input from the user.

To understand this example, you should have the knowledge of following Python programming topics:

```
''' Program make a simple calculator that can add, subtract, multiply and divide using functions '''
# This function adds two numbers
def add(x, y):
return x + y
# This function subtracts two numbers
def subtract(x, y):
return x - y
# This function multiplies two numbers
def multiply(x, y):
return x * y
# This function divides two numbers
def divide(x, y):
return x / y
print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")
# Take input from the user
choice = input("Enter choice(1/2/3/4):")
num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
if choice == '1':
print(num1,"+",num2,"=", add(num1,num2))
elif choice == '2':
print(num1,"-",num2,"=", subtract(num1,num2))
elif choice == '3':
print(num1,"*",num2,"=", multiply(num1,num2))
elif choice == '4':
print(num1,"/",num2,"=", divide(num1,num2))
else:
print("Invalid input")
```

**Output**

Select operation. 1.Add 2.Subtract 3.Multiply 4.Divide Enter choice(1/2/3/4): 3 Enter first number: 15 Enter second number: 14 15 * 14 = 210

In this program, we ask the user to choose the desired operation. Options 1, 2, 3 and 4 are valid. Two numbers are taken and an `if...elif...else`

branching is used to execute a particular section. User-defined functions `add()`

, `subtract()`

, `multiply()`

and `divide()`

evaluate respective operations.