C#字符串操作问题

string str1 = "Hello";
string str2 = "World";
string result = str1 + " " + str2;
Console.WriteLine(result);  // output: "Hello World"

string name = "John";
int age = 25;
string result = String.Format("My name is {0} and I am {1} years old.", name, age);
Console.WriteLine(result);  // output: "My name is John and I am 25 years old."

string str = "Hello World";
int start = 3;
int length = 5;
string result = str.Substring(start, length);
Console.WriteLine(result);  // output: "llo Wo"

string str = "Hello World";
string newStr = str.Replace("World", "Universe");
Console.WriteLine(newStr);  // output: "Hello Universe"