以下是一个简单的编程案例，用Python语言编写一个计算器程序：
```python
# 计算器程序
def add(x, y):
"""相加"""
return x + y
def subtract(x, y):
"""相减"""
return x - y
def multiply(x, y):
"""相乘"""
return x * y
def divide(x, y):
"""相除"""
if y == 0:
raise ValueError("除数不能为0")
return x / y
# 用户输入
num1 = float(input("请输入第一个数字: "))
num2 = float(input("请输入第二个数字: "))
print("请选择操作:")
print("1. 相加")
print("2. 相减")
print("3. 相乘")
print("4. 相除")
choice = input("请输入您的选择(1/2/3/4): ")
if choice == '1':
print(num1, "+", num2, "=", add(num1, num2))
elif choice == '2':
print(num1, "-", num2, "=", subtract(num1, num2))
elif choice == '3':
print(num1, "*", num2, "=", multiply(num1, num2))
elif choice == '4':
print(num1, "/", num2, "=", divide(num1, num2))
else:
print("非法输入")
```
