程序设计 (4)

### 1. Python 示例（计算两个数的和）
```python
def add_numbers(a, b):
    return a + b
 
result = add_numbers(5, 3)
print("The result is:", result)
```
 
### 2. Java 示例（打印 "Hello, World!"）
```java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}
```
 
### 3. JavaScript 示例（网页上的交互）
```javascript
document.addEventListener('DOMContentLoaded', function() {
    document.getElementById('greeting').textContent = 'Hello, World!';
});
```
假设有一个HTML元素的ID是`greeting`。
 
### 4. C 示例（计算数组的平均值）
```c
#include <stdio.h>
 
int main() {
    int numbers[] = {1, 2, 3, 4, 5};
    int sum = 0;
    int i;
    for (i = 0; i < sizeof(numbers) / sizeof(numbers[0]); i++) {
        sum += numbers[i];
    }
    float average = (float)sum / i;
    printf("The average is: %f\n", average);
    return 0;
}
```
 
### 5. C# 示例（简单的类和对象）
```csharp
using System;
 
class Circle {
    public double Radius { get; set; }
    public double CalculateArea() {
        return Math.PI * Math.Pow(Radius, 2);
    }
}
 
class Program {
    static void Main() {
        Circle circle = new Circle { Radius = 5 };
        Console.WriteLine("Area: " + circle.CalculateArea());
    }
}
```
 
### 6. Ruby 示例（字符串反转）
```ruby
def reverse_string(str)
    str.reverse
end
 
puts reverse_string("hello")  # Outputs: "olleh"
```
 
### 7. PHP 示例（简单的网页输出）
```php
<?php
echo "Hello, World!";
?>
```
 
### 8. Go 示例（并发服务器）
```go
package main
 
import (
    "fmt"
    "net/http"
)
 
func handler(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "Hello, World!")
}
 
func main() {
    http.HandleFunc("/", handler)
    http.ListenAndServe(":8080", nil)
}
```