Putting it together
- Python course
- Beginner
- Lesson 23/116
- 6 min
Write a working calculator with menu loop.
Putting the calculator together
In the final lesson we combine the calculator. All functions are ready; now we'll add an operator choice. We'll use an if/elif structure to apply the selected operation:
operator = "+"
if operator == "+":
print(add(a, b))
elif operator == "-":
print(subtract(a, b))if/elif tries several conditions in order; the first true block runs. We'll cover this structure in detail in a separate group.
The complete calculator
Now we combine all the pieces. We'll assign an operation to the operator variable and call the related function with if/elif:
operator = "*"
if operator == "+":
print(add(a, b))
elif operator == "-":
print(subtract(a, b))
elif operator == "*":
print(multiply(a, b))
elif operator == "/":
print(divide(a, b))This is the skeleton of the calculator. In a real app the operator comes from the user; here we test with a fixed value.
Practice Complete the calculator
All functions are ready. Assign operator = "*". Then use if/elif to compare the four operations in order: + calls add, - calls subtract, * calls multiply, / calls divide, and print the result.
Starter code
# Calculator - define two numbers
a = 10
b = 5
def add(x, y):
return x + y
def subtract(x, y):
return x - y
def multiply(x, y):
return x * y
def divide(x, y):
try:
return x / y
except ZeroDivisionError:
return 0
# Choose an operator and perform the operationSample solution
operator = "*"
if operator == "+":
print(add(a, b))
elif operator == "-":
print(subtract(a, b))
elif operator == "*":
print(multiply(a, b))
elif operator == "/":
print(divide(a, b))Expected output
50
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which block runs in an if/elif structure?
- The first true condition's block Correct answer
- All blocks
- The last block
- None
Explanation: if/elif runs the first true condition's block.
2 Complete the operator comparison
if operator ____ "+":
print(add(a, b))if operator == "+":
print(add(a, b))Explanation: == is the equality comparison.
3 Match the calculator pieces
| Term | Meaning |
|---|---|
def |
Function definition |
if/elif |
Operator choice |
try/except |
Error catching |
print |
Printing the result |