Code Editor for app.py

# calculator_app.py
"""
A calculator app with buttons like a traditional calculator.
Run with: streamlit run calculator_app.py
"""

import streamlit as st

# Page configuration
st.set_page_config(
    page_title="Calculator App",
    page_icon="🧮",
    layout="centered"
)

# Initialize session state variables
if 'display' not in st.session_state:
    st.session_state.display = "0"
if 'previous' not in st.session_state:
    st.session_state.previous = None
if 'operation' not in st.session_state:
    st.session_state.operation = None
if 'should_reset_display' not in st.session_state:
    st.session_state.should_reset_display = False
if 'equation' not in st.session_state:
    st.session_state.equation = ""

def handle_number(num):
    """Handle number button clicks"""
    if st.session_state.should_reset_display or st.session_state.display == "0":
        st.session_state.display = str(num)
        st.session_state.should_reset_display = False
    else:
        # Limit display length to prevent overflow
        if len(st.session_state.display) < 12:
            st.session_state.display += str(num)

def handle_decimal():
    """Handle decimal point button"""
    if st.session_state.should_reset_display:
        st.session_state.display = "0."
        st.session_state.should_reset_display = False
    elif "." not in st.session_state.display:
        st.session_state.display += "."

def handle_operation(op):
    """Handle operation buttons (+, -, ×, ÷)"""
    # If there's a previous operation pending, calculate it first
    if st.session_state.previous is not None and st.session_state.operation is not None and not st.session_state.should_reset_display:
        calculate()
    
    st.session_state.previous = float(st.session_state.display)
    st.session_state.operation = op
    st.session_state.should_reset_display = True
    st.session_state.equation = f"{st.session_state.display} {op}"

def calculate():
    """Perform the calculation"""
    if st.session_state.previous is None or st.session_state.operation is None:
        return
    
    current = float(st.session_state.display)
    prev = st.session_state.previous
    op = st.session_state.operation
    
    try:
        if op == "+":
            result = prev + current
        elif op == "-":
            result = prev - current
        elif op == "×":
            result = prev * current
        elif op == "÷":
            if current == 0:
                st.session_state.display = "Error"
                st.session_state.previous = None
                st.session_state.operation = None
                st.session_state.should_reset_display = True
                return
            result = prev / current
        
        # Format result nicely
        if result.is_integer() and -1e12 < result < 1e12:
            st.session_state.display = str(int(result))
        else:
            # Limit decimal places and use scientific notation for very large/small numbers
            if abs(result) > 1e12 or (abs(result) < 1e-6 and result != 0):
                st.session_state.display = f"{result:.6e}"
            else:
                st.session_state.display = f"{result:.10g}"  # Remove trailing zeros
        
        st.session_state.equation = f"{prev} {op} {current} ="
        
    except OverflowError:
        st.session_state.display = "Overflow"
    except Exception:
        st.session_state.display = "Error"
    
    st.session_state.previous = None
    st.session_state.operation = None
    st.session_state.should_reset_display = True

def clear_all():
    """Clear all calculator state"""
    st.session_state.display = "0"
    st.session_state.previous = None
    st.session_state.operation = None
    st.session_state.should_reset_display = False
    st.session_state.equation = ""

def clear_entry():
    """Clear current entry only"""
    st.session_state.display = "0"
    st.session_state.should_reset_display = False

def backspace():
    """Remove last digit"""
    if not st.session_state.should_reset_display and st.session_state.display not in ["Error", "Overflow"]:
        if len(st.session_state.display) > 1:
            st.session_state.display = st.session_state.display[:-1]
        else:
            st.session_state.display = "0"

def toggle_sign():
    """Toggle positive/negative"""
    if st.session_state.display not in ["Error", "Overflow", "0"]:
        if st.session_state.display.startswith("-"):
            st.session_state.display = st.session_state.display[1:]
        else:
            st.session_state.display = "-" + st.session_state.display

# UI Layout
st.title("🧮 Calculator")

# Display area with equation and result
display_container = st.container()
with display_container:
    # Show the equation being built
    st.caption(st.session_state.equation if st.session_state.equation else " ")
    
    # Main display with custom styling
    st.markdown(
        f"""
        <div style="
            
            padding: 20px;
            border-radius: 10px;
            text-align: right;
            font-size: 2em;
            font-family: 'Courier New', monospace;
            min-height: 60px;
            margin-bottom: 20px;
            word-wrap: break-word;
            overflow-wrap: break-word;
        ">
            {st.session_state.display}
        </div>
        """,
        unsafe_allow_html=True
    )

# Calculator button layout
# Row 1: Clear functions
col1, col2, col3, col4 = st.columns(4)
with col1:
    st.button("C", on_click=clear_all, use_container_width=True, help="Clear All")
with col2:
    st.button("CE", on_click=clear_entry, use_container_width=True, help="Clear Entry")
with col3:
    st.button("⌫", on_click=backspace, use_container_width=True, help="Backspace")
with col4:
    st.button("÷", on_click=lambda: handle_operation("÷"), use_container_width=True, type="secondary")

# Row 2: 7, 8, 9, ×
col1, col2, col3, col4 = st.columns(4)
with col1:
    st.button("7", on_click=lambda: handle_number(7), use_container_width=True)
with col2:
    st.button("8", on_click=lambda: handle_number(8), use_container_width=True)
with col3:
    st.button("9", on_click=lambda: handle_number(9), use_container_width=True)
with col4:
    st.button("×", on_click=lambda: handle_operation("×"), use_container_width=True, type="secondary")

# Row 3: 4, 5, 6, -
col1, col2, col3, col4 = st.columns(4)
with col1:
    st.button("4", on_click=lambda: handle_number(4), use_container_width=True)
with col2:
    st.button("5", on_click=lambda: handle_number(5), use_container_width=True)
with col3:
    st.button("6", on_click=lambda: handle_number(6), use_container_width=True)
with col4:
    st.button("-", on_click=lambda: handle_operation("-"), use_container_width=True, type="secondary")

# Row 4: 1, 2, 3, +
col1, col2, col3, col4 = st.columns(4)
with col1:
    st.button("1", on_click=lambda: handle_number(1), use_container_width=True)
with col2:
    st.button("2", on_click=lambda: handle_number(2), use_container_width=True)
with col3:
    st.button("3", on_click=lambda: handle_number(3), use_container_width=True)
with col4:
    st.button("+", on_click=lambda: handle_operation("+"), use_container_width=True, type="secondary")

# Row 5: +/-, 0, ., =
col1, col2, col3, col4 = st.columns(4)
with col1:
    st.button("+/-", on_click=toggle_sign, use_container_width=True)
with col2:
    st.button("0", on_click=lambda: handle_number(0), use_container_width=True)
with col3:
    st.button(".", on_click=handle_decimal, use_container_width=True)
with col4:
    st.button("=", on_click=calculate, use_container_width=True, type="primary")

# Additional scientific functions (optional row)
st.markdown("---")
st.caption("🔬 Scientific Functions")

col1, col2, col3, col4 = st.columns(4)
with col1:
    if st.button("x²", use_container_width=True):
        try:
            val = float(st.session_state.display)
            result = val ** 2
            st.session_state.display = str(int(result)) if result.is_integer() else f"{result:.10g}"
            st.session_state.equation = f"{val}² ="
            st.session_state.should_reset_display = True
        except:
            st.session_state.display = "Error"

with col2:
    if st.button("√x", use_container_width=True):
        try:
            val = float(st.session_state.display)
            if val < 0:
                st.session_state.display = "Error"
            else:
                result = val ** 0.5
                st.session_state.display = str(int(result)) if result.is_integer() else f"{result:.10g}"
                st.session_state.equation = f"√{val} ="
            st.session_state.should_reset_display = True
        except:
            st.session_state.display = "Error"

with col3:
    if st.button("1/x", use_container_width=True):
        try:
            val = float(st.session_state.display)
            if val == 0:
                st.session_state.display = "Error"
            else:
                result = 1 / val
                st.session_state.display = f"{result:.10g}"
                st.session_state.equation = f"1/{val} ="
            st.session_state.should_reset_display = True
        except:
            st.session_state.display = "Error"

with col4:
    if st.button("%", use_container_width=True):
        try:
            val = float(st.session_state.display)
            result = val / 100
            st.session_state.display = f"{result:.10g}"
            st.session_state.equation = f"{val}% ="
            st.session_state.should_reset_display = True
        except:
            st.session_state.display = "Error"

# Footer
st.markdown("---")
st.caption("💡 **Tip:** Click the buttons to perform calculations just like a traditional calculator!")

# Add custom CSS for better button styling
st.markdown("""
<style>
    /* Make buttons taller */
    .stButton > button {
        height: 60px;
        font-size: 20px;
        font-weight: bold;
    }
    
    /* Style operation buttons */
    .stButton > button[kind="secondary"] {
        background-color: #ff6b6b;
        color: white;
    }
    
    /* Style equals button */
    .stButton > button[kind="primary"] {
        background-color: #4CAF50;
        color: white;
    }
</style>
""", unsafe_allow_html=True)