如何在 C# 中比较字符串？

原文:https://www . geesforgeks . org/c-sharp 中字符串的比较方法/

字符串是字符的集合，用于存储纯文本。与 C 或 C++不同，C# 中的字符串不以空字符结尾。字符串对象的最大大小取决于系统的内部架构。后面跟“string”的变量实际上是 string 类的对象。

如何实例化一个字符串对象？

我们可以通过使用变量名称后跟“字符串”关键字来创建字符串类的对象。

语法:

串密音；

我们也可以在声明时初始化一个字符串对象。

语法:

字符串 mystring = " geeksforgeeks

本文主要讨论如何在 C# 中比较字符串。比如给我们三个字符串“极客 forGeeks”“极客”和“极客 forGeeks”。显然第一个和最后一个字符串是相同的。在 C# 中有许多比较字符串的方法，下面将详细解释其中的五种方法。

方法 1:使用字符串。Equals()方法

中指定了字符串类。NET 基类库。换句话说，字符串对象是系统的顺序集合。代表字符串的字符对象。系统。字符串类是不可变的，也就是说，一旦创建了它的状态，我们就不能对它进行更改。字符串。Equals()方法是 String 类的一种方法。此方法将两个字符串作为参数进行比较。它返回一个逻辑值，真或假，借助它我们可以确定给定的字符串是否相同。

语法:

字符串。等于(我的字符串 1，我的字符串 2)

参数:取两个参数 myString1:第一个字符串，myString2:第二个字符串

返回类型:该方法的返回类型为布尔型。如果两个字符串相等，则为真；如果两个字符串不同，则为假

示例:

C

// C# program to illustrate the working of
// String.Equals() method to compare two strings
using System;

class GFG{

static public void Main()
{

    // Initialize a string
    string myString1 = "GeeksforGeeks"; 

    // Initialize another string
    string myString2 = "Geeks";

    // Initialize a string
    string myString3 = "GeeksforGeeks";

    // If this method returns true
    // Print both string are same
    if (String.Equals(myString1, myString2)) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If this method returns false
    // Print both string are different
    else 
        Console.WriteLine({content}quot;{myString1} and {myString2} are different."); 

    // If this method returns true
    // Print both string are same
    if (String.Equals(myString1, myString3)) 
        Console.WriteLine({content}quot;{myString1} and {myString3} are same."); 

    // If this method returns false
    // Print both string are different
    else 
        Console.WriteLine({content}quot;{myString1} and {myString3} are different."); 

    // If this method returns true
    // Print both string are same
    if (String.Equals(myString2, myString3)) 
        Console.WriteLine({content}quot;{myString2} and {myString3} are same."); 

    // If this method returns false
    // Print both string are different
    else 
        Console.WriteLine({content}quot;{myString2} and {myString3} are different.");          
}
}

Output

GeeksforGeeks and Geeks are different.
GeeksforGeeks and GeeksforGeeks are same.
Geeks and GeeksforGeeks are different.

方法 2:使用字符串。Compare()方法

该方法也在 String 类下定义。此方法还将两个要比较的字符串作为参数。它根据传递给方法的字符串返回一个数值。这个方法提供了字符串比较的详细信息，这就是为什么它比 String.equals() 方法更有优势。

语法:

字符串。比较(myString1、myString2)

参数:取两个参数 myString1:第一个字符串，myString2:第二个字符串

返回类型:该方法的返回类型为 Integer。它将是:

  • 小于零:如果第一个字符串在字典序上小于第二个字符串。
  • 零:如果两个字符串相等。
  • 大于零:如果第一个字符串在字典序上大于第二个字符串。

示例:

C

// C# program to illustrate the working of
// String.Compare() method to compare two strings
using System;

class GFG{

static public void Main()
{

    // Initialize a string
    string myString1 = "GeeksforGeeks"; 

    // Initialize another string
    string myString2 = "Geeks";

    // Initialize another string
    string myString3 = "GeeksforGeeks";

    // If value returned by this method is equal to 0
    // Print both string are same
    if (String.Compare(myString1, myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If value returned by this method is less than 0
    // Then print first string is smaller than the second string
    else if(String.Compare(myString1, myString2) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString2}."); 

    // If value returned bu the method is greater than 0
    // Then print first string is greater than the second string
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString2}."); 

    // If value returned by this method is equal to 0
    // Print both string are same     
    if (String.Compare(myString1, myString3) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString3} are same."); 

    // If value returned by this method is less than 0
    // Then print first string is smaller than the second string
    else if (String.Compare(myString1, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString3}."); 

    // If value returned bu the method is greater than 0
    // Then print first string is greater than the second string
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString3}."); 

    // If value returned by this method is equal to 0
    // Print both string are same           
    if (String.Compare(myString2, myString3) == 0) 
        Console.WriteLine({content}quot;{myString2} and {myString3} are same."); 

    // If value returned by this method is less than 0
    // Then print first string is smaller than the second string
    else if (String.Compare(myString2, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically smaller than {myString3}."); 

    // If value returned bu the method is greater than 0
    // Then print first string is greater than the second string      
    else
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically greater than {myString3}."); 
}
}

Output

GeeksforGeeks is lexicographically greater than Geeks.
GeeksforGeeks and GeeksforGeeks are same.
Geeks is lexicographically smaller than GeeksforGeeks.

方法 3:使用 CompareTo()方法

这是在字符串类下定义的实例方法，它直接应用于字符串或字符串对象。它根据要比较的字符串返回一个数值。这个方法提供了字符串比较的详细信息，这就是为什么它比 String.equals() 方法更有优势。

语法:

神秘 1 号。共享(myString2)

参数:取一个参数，就是 myString2:第二个字符串

返回类型:该方法的返回类型为 Integer。它将是:

  • 小于零:如果第一个字符串在字典序上小于第二个字符串。
  • 零:如果两个字符串相等。
  • 大于零:如果第一个字符串在字典序上大于第二个字符串。

示例:

C

// C# program to illustrate the working of
// CompareTo() method to compare two strings
using System;

class GFG{

static public void Main()
{

    // Initialize a string
    string myString1 = "GeeksforGeeks"; 

    // Initialize another string
    string myString2 = "Geeks"; 

    // Initialize another string
    string myString3 = "GeeksforGeeks";

    // If value returned by this method is equal to 0
    // Then display both strings are equal
    if (myString1.CompareTo(myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If value returned by this method is less than 0
    // Then print the first string is smaller than the second string
    else if (myString1.CompareTo(myString2) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString2}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string      
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString2}."); 

    // If value returned by this method is equal to 0
    // Then print both strings are equal      
    if (myString1.CompareTo(myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString3} are same."); 

    // If value returned by this method is less than 0
    // Then print the first string is smaller than the second string      
    else if(myString1.CompareTo(myString2) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString3}."); 

    // If value returned by this method is equal to 0
    // Then display both strings are equal        
    if (myString1.CompareTo(myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If value returned by this method is less than 0
    // Then print the first string is smaller than the second string 
    else if (myString1.CompareTo(myString2) < 0)
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string
    else
    Console.WriteLine(
        {content}quot;{myString2} is lexicographically greater than {myString3}."); 
}
}

Output

GeeksforGeeks is lexicographically greater than Geeks.
GeeksforGeeks is lexicographically greater than GeeksforGeeks.
Geeks is lexicographically greater than GeeksforGeeks.

方法 4:使用 StringComparer 类的 compare()方法

这个方法是在 StringComparer 类下定义的。我们可以创建这个类的一个对象，在这个对象的帮助下，我们可以使用 Compare()方法来比较两个字符串。这个方法提供了字符串比较的详细信息，这就是为什么它比 String.equals() 方法更有优势。

语法:

string compare my company = string compare-字串比较。序数忽略；

支原体感染。比较(myString1、mystring 2)；

参数:取两个参数 myString1:第一个字符串，myString2:第二个字符串

返回类型:该方法的返回类型为 Integer。它将是:

  • 小于零:如果第一个字符串在字典序上小于第二个字符串。
  • 零:如果两个字符串相等。
  • 大于零:如果第一个字符串在字典序上大于第二个字符串。

示例:

C

// C# program to illustrate the working of Compare() method
// of StringComparer class to compare two strings
using System;

class GFG{

static public void Main()
{

    // Declare an object of class StringComparer
    StringComparer myComparer = StringComparer.OrdinalIgnoreCase;

    // Initialize a string
    string myString1 = "GeeksforGeeks";

    // Initialize another string
    string myString2 = "Geeks";

    // Initialize another string
    string myString3 = "GeeksforGeeks";

    // Compare strings using Compare method
    // on the instantiated object

    // If this method returns 0
    // Print both strings are same
    if (myComparer.Compare(myString1, myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string    
    else if (myComparer.Compare(myString1, myString2) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString2}."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string  
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString2}."); 

    // If this method returns 0
    // Print both strings are same     
    if (myComparer.Compare(myString1, myString3) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString3} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string 
    else if (myComparer.Compare(myString1, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString3}."); 

    // If this method returns 0
    // Print both strings are same           
    if (myComparer.Compare(myString2, myString3) == 0) 
        Console.WriteLine({content}quot;{myString2} and {myString3} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string       
    else if (myComparer.Compare(myString2, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string
    else
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically greater than {myString3}."); 
}
}

Output

GeeksforGeeks is lexicographically greater than Geeks.
GeeksforGeeks and GeeksforGeeks are same.
Geeks is lexicographically smaller than GeeksforGeeks.

方法 5:逐个字符比较(使用自定义比较方法)

字符串可以逐个字符进行比较。按照以下步骤使用自定义比较方法比较两个字符串。

  1. 声明一个静态方法比较主方法之外的。将此方法的返回类型设置为 int。
  2. 将变量 len 初始化为两个字符串长度的最小值。
  3. 使用 for 循环迭代索引= 0 到索引= len–1。每次迭代时，比较字符串的相应字符。
  4. 如果第一个字符串在索引处的第一个不匹配字符小于第二个字符串在索引处的字符，那么我们将返回-1。
  5. 如果第一个字符串在索引处的第一个不匹配字符小于第二个字符串在索引处的字符，那么我们将返回 1。
  6. 在 for 循环结束后，如果两个字符串的长度相等，则返回 0。如果第一个字符串的长度小于第二个字符串，则返回-1，否则返回 1。
  7. 通过传递要比较的字符串作为参数，从主函数调用 Compare() 函数。如果比较()函数返回 0，则打印第一个字符串与第二个字符串相同。如果比较()函数返回-1，则打印第一个字符串小于第二个字符串，否则打印第一个字符串大于第二个字符串。

示例:

C

// C# program to illustrate the working of
// custom Compare() method to compare two strings
using System;

class GFG{

// Compare method to compare two strings
static public int Compare(string myString1, string myString2)
{

    // len stores minimum of two string lengths
    int len = Math.Min(myString1.Length, myString2.Length);

    // Iterate over all characters
    for(int index = 0; index < len; index++)
    {

        // If the first not matched character of first
        // string is smaller than the second string then
        // return -1
        if (myString1[index] < myString2[index])
            return -1;

        // If the first not matched character of first
        // string is greater than the second string then
        // return 1         
        else if (myString1[index] > myString2[index])
            return 1;
    }

    // If lengths are equal
    // Return 0
    if (myString1.Length ==  myString2.Length)
        return 0;

    // If length of first string is smaller than the second string
    // then return -1
    // If length of first string is greater than the second string
    // then return 1
    return ((myString1.Length <  myString2.Length) ? -1 : 1);
}

// Driver code
static public void Main()
{

    // Initialize a string
    string myString1 = "GeeksforGeeks"; 

    // Initialize another string
    string myString2 = "Geeks"; 

    // Initialize another string
    string myString3 = "GeeksforGeeks";

    // If value returned by this method is equal to 0
    // Then print both strings are same          
    if (Compare(myString1, myString2) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString2} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string
    else if (Compare(myString1, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString2}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string      
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString2}.");

    // If value returned by this method is equal to 0
    // Then print both strings are same         
    if (Compare(myString1, myString3) == 0) 
        Console.WriteLine({content}quot;{myString1} and {myString3} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string      
    else if (Compare(myString1, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string 
    else
        Console.WriteLine(
            {content}quot;{myString1} is lexicographically greater than {myString3}.");

    // If value returned by this method is equal to 0
    // Then print both strings are same             
    if (Compare(myString2, myString3) == 0) 
        Console.WriteLine({content}quot;{myString2} and {myString3} are same."); 

    // If value returned by this method is smaller than 0
    // Then print the first string is smaller than the second string
    else if (Compare(myString2, myString3) < 0)
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically smaller than {myString3}."); 

    // If value returned by this method is greater than 0
    // Then print the first string is greater than the second string 
    else
        Console.WriteLine(
            {content}quot;{myString2} is lexicographically greater than {myString3}.");
}
}

Output

GeeksforGeeks is lexicographically greater than Geeks.
GeeksforGeeks and GeeksforGeeks are same.
Geeks is lexicographically smaller than GeeksforGeeks.

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