app.py

import streamlit as st

# Define backend functions for calculations
def add(a, b):
    return a + b

def subtract(a, b):
    return a - b

def multiply(a, b):
    return a * b

def divide(a, b):
    if b != 0:
        return a / b
    else:
        return "Error! Division by zero."

# Streamlit frontend
st.title("Simple Calculator")

st.write("Choose operation:")
operation = st.selectbox("Operation", ("Add", "Subtract", "Multiply", "Divide"))

num1 = st.number_input("Enter first number", value=0.0, format="%f")
num2 = st.number_input("Enter second number", value=0.0, format="%f")

if st.button("Calculate"):
    if operation == "Add":
        result = add(num1, num2)
    elif operation == "Subtract":
        result = subtract(num1, num2)
    elif operation == "Multiply":
        result = multiply(num1, num2)
    elif operation == "Divide":
        result = divide(num1, num2)

    st.write(f"Result: {result}")