对string如何查询莫个元素是否存在

在大多数编程语言中，如果你想要查询一个 `string`（字符串）中是否包含特定的元素（通常是字符），可以使用以下几个方法：

1. **Python**:

   if 'target_char' in my_string:
       print(f"'{target_char}' exists in the string.")
   else:
       print(f"'{target_char}' does not exist in the string.")

2. **Java** (Java 8及以上版本):

   boolean found = myString.contains("target_char");
   if (found) {
       System.out.println("Target character exists in the string.");
   } else {
       System.out.println("Target character does not exist in the string.");
   }

3. **C#**:

   bool contains = myString.Contains("target_char");
   Console.WriteLine(contains ? "Target character exists" : "Target character does not exist");

4. **JavaScript**:

   const index = myString.indexOf("target_char");
   if (index !== -1) {
       console.log(`"${target_char}" exists at position ${index}`);
   } else {
       console.log("'target_char' does not exist in the string.");
   }

5. **C++** (使用 C++17 以上的范围基础 for 循环):

   std::string_view sv(my_string);
   if (sv.find("target_char") != std::string_view::npos) {
       std::cout << "Target character exists in the string.";
   } else {
       std::cout << "Target character does not exist in the string.";
   }

6. **PHP**:

   if (strpos($my_string, "target_char") !== false) {
       echo "'$target_char' exists in the string.";
   } else {
       echo "'$target_char' does not exist in the string.";
   }

以上代码片段都是检查给定的 `string` 是否包含指定的字符，并打印相应的消息。如果没有找到，会返回布尔值 `false` 或相应提示。