diff --git a/.gitignore b/.gitignore
index 5d2b7d35..695f3ca5 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,4 +2,4 @@
 **/*.pyc
 **/.DS_Store
 .coverage
-venv/
\ No newline at end of file
+venv/
diff --git a/src/calculator.py b/src/calculator.py
index 5eb03460..622475e3 100644
--- a/src/calculator.py
+++ b/src/calculator.py
@@ -1,12 +1,24 @@
-#
-#   Write a program that given two numbers as input make the main operations.
-#
-#   Output:
-#   Insert first number: 4
-#   Insert second number: 2
-#
-#   SUM: 6
-#   Difference: 2
-#   Multiplication: 8
-#   Division: 2
-#
+def add(a: int, b: int) -> int:
+    return a + b
+
+
+def sub(a: int, b: int) -> int:
+    return a - b
+
+
+def mul(a: int, b: int) -> int:
+    return a * b
+
+
+def div(a: int, b: int) -> float | str:
+    return "You can't divide by 0" if b == 0 else a / b
+
+
+if __name__ == "__main__":
+    x = int(input("Insert first number: "))
+    y = int(input("Insert second number: "))
+
+    print(f"Sum of {x} and {y} = {add(x, y)}")
+    print(f"Subtraction of {x} and {y} = {sub(x, y)}")
+    print(f"Multiplication of {x} and {y} = {mul(x, y)}")
+    print(f"Division of {x} and {y} = {div(x, y)}")
diff --git a/tests/test_calculator.py b/tests/test_calculator.py
new file mode 100644
index 00000000..ee52ae83
--- /dev/null
+++ b/tests/test_calculator.py
@@ -0,0 +1,25 @@
+from src.calculator import add, div, mul, sub
+
+
+def test_add() -> None:
+    assert add(5, 4) == 9
+    assert add(-1, 1) == 0
+    assert add(0, 0) == 0
+
+
+def test_sub() -> None:
+    assert sub(1, 1) == 0
+    assert sub(0, 5) == -5
+
+
+def test_mul() -> None:
+    assert mul(5, 1) == 5
+    assert mul(0, 5) == 0
+    assert mul(-2, 3) == -6
+
+
+def test_div() -> None:
+    assert div(5, 1) == 5
+    assert div(0, 5) == 0
+    assert div(5, 0) == "You can't divide by 0"
+    assert div(-6, 2) == -3