单利计算器

def simple_interest(principal: float, rate: float, time: float) -> dict:
    """
    Calculate simple interest.
    principal: initial amount
    rate: annual interest rate as percentage (e.g. 5 for 5%)
    time: time in years
    """
    interest = principal * (rate / 100) * time
    total = principal + interest
    return {
        "principal": principal,
        "interest": interest,
        "total": total,
        "rate": rate,
        "time": time,
    }

# Example
result = simple_interest(principal=1000, rate=5, time=3)
print(f"Principal:  ${result['principal']:,.2f}")
print(f"Interest:   ${result['interest']:,.2f}")
print(f"Total:      ${result['total']:,.2f}")

# Compare with compound interest
def compound_interest(principal: float, rate: float, time: float, n: int = 1) -> float:
    """n = compounding periods per year."""
    return principal * (1 + rate / 100 / n) ** (n * time)

ci_total = compound_interest(1000, 5, 3)
print(f"\nCompound interest total: ${ci_total:,.2f}")
print(f"Difference (CI - SI):    ${ci_total - result['total']:,.2f}")