CSharp-Learning/notes/03_Conditions_and_Loops.md

# 第三课：条件判断和循环

## if / else 判断

```csharp
int score = 85;

if (score >= 90)
{
    Console.WriteLine("优秀");
}
else if (score >= 60)
{
    Console.WriteLine("及格");
}
else
{
    Console.WriteLine("不及格");
}

// 三元运算符（简单判断）
string result = score >= 60 ? "及格" : "不及格";
```

## switch 选择

```csharp
int day = 3;

switch (day)
{
    case 1:
        Console.WriteLine("星期一");
        break;
    case 2:
        Console.WriteLine("星期二");
        break;
    case 3:
        Console.WriteLine("星期三");
        break;
    default:
        Console.WriteLine("其他");
        break;
}
```

## for 循环

```csharp
// 传统 for
for (int i = 0; i < 5; i++)
{
    Console.WriteLine(i);
}

// 遍历数组
string[] names = { "A", "B", "C" };
for (int i = 0; i < names.Length; i++)
{
    Console.WriteLine(names[i]);
}
```

## foreach 循环（更简洁）

```csharp
string[] names = { "A", "B", "C" };

foreach (string name in names)
{
    Console.WriteLine(name);
}
```

## while 循环

```csharp
int i = 0;
while (i < 5)
{
    Console.WriteLine(i);
    i++;
}

// 先执行再判断
do
{
    Console.WriteLine(i);
    i++;
} while (i < 5);
```

## break 和 continue

```csharp
for (int i = 0; i < 10; i++)
{
    if (i == 3) continue;  // 跳过 i=3
    if (i == 7) break;     // 退出循环
    Console.WriteLine(i);
}
```