C＃中双引号和单引号之间的区别是什么

Question

What's the difference between double quotes and single quote in C#?

I coded a program to count how many words are in a file

using System;
using System.IO;
namespace Consoleapp05
{
    class Program
    {
        public static void Main(string[] args)
        {
            StreamReader sr = new StreamReader(@"C:\words.txt");
            string text = sr.ReadToEnd();
            int howmany = 0;
            int howmany2 = 0;

            for(int i = 0; i < text.Length; i++)
            {
                if(text[i] == " ")
                {
                howmany++;
                }
            }
            howmany2 = howmany + 1;
            Console.WriteLine("It is {0} words in the file", howmany2);
            Console.ReadKey(true);
        }
    }
}

This gives me an error because of the double quotes. My teacher told me to use single quote instead, but he didn't tell me why. So what's the difference between double quotes and single quote in C#?

Answer 1

Single quotes encode a single character (data type char ), while double quotes encode a string of multiple characters. The difference is similar to the difference between a single integer and an array of integers.

char c = 'c';
string s = "s"; // String containing a single character.
System.Diagnostics.Debug.Assert(s.Length == 1);
char d = s[0];

int i = 42;
int[] a = new int[] { 42 }; // Array containing a single int.
System.Diagnostics.Debug.Assert(a.Length == 1);
int j = a[0];

Answer 2

when you say string s = "this string" then s[0] is a char at at specific index in that string (in this case s[0] == 't')

So to answer your question, use double quotes or single quotes, you can think of the following as meaning the same thing:

string s = " word word";

// check for space as first character using single quotes
if(s[0] == ' ') {
 // do something
}

// check for space using string notation
if(s[0] == " "[0]) {
 // do something
}

As you can see, using a single quote to determine a single char is a lot easier than trying to convert our string into a char just for testing.

if(s[0] == " "[0]) { 
 // do something
}

is really like saying:

string space = " ";
if(s[0] == space[0]) {
 // do something
}

Hopefully I did not confuse you more!

Answer 3

单引号表示单个字符'A' ，双引号将空终结符'\\0'附加到字符串文字的末尾， " "实际上是" \\0" ，它比预期大小大一个字节。

Answer 4

Single quotes instead of double ones?

Where? Here? if(text[i] == " ")

text[i] gives a character/byte and this is compared to an array of (probably unicoded ??) characters/bytes. That does not work well.

Say: compare '1' with 1
or "1" with "one" or (2-1) with "eins" what do you think are the correct answers, or is there no meaningful answer anyway?

Besides that: the program will not work very well with single quotes either, given the example "words.txt" =

one word or 2 words or more words here ?

Answer 5

you are looking for spaces, this can be done as a space in a string or as a char. So in my opinion this would work.

(By the way, if the file contains sentences with dots. And someone forgot to add a space after the dot, the word will not be added to the total amount of words)