# File: app.py
import streamlit as st

def calculate(num1, num2, operation):
    if operation == 'Add':
        return num1 + num2
    elif operation == 'Subtract':
        return num1 - num2
    elif operation == 'Multiply':
        return num1 * num2
    elif operation == 'Divide':
        if num2 != 0:
            return num1 / num2
        else:
            return "Error: Division by zero"

def main():
    st.title('Simple Calculator')
    
    # Input for first number
    num1 = st.number_input('Enter first number', value=0.0)
    
    # Operation selection
    operation = st.selectbox('Select operation', 
                             ['Add', 'Subtract', 'Multiply', 'Divide'])
    
    # Input for second number
    num2 = st.number_input('Enter second number', value=0.0)
    
    # Calculate button
    if st.button('Calculate'):
        result = calculate(num1, num2, operation)
        st.success(f'Result: {result}')

if __name__ == '__main__':
    main()