Question

有人可以向我解释为什么这段代码不会执行while条件？我只是想知道为什么代码会以这种方式运行，或者是否有其他方法可以使它工作。谢谢

UPDATE !!!

嗨顺便说一下这是代码，我对C ++不是很熟悉，所以我不确定程序是否会在开关上跳过while条件。谢谢

#include<iostream>
#include<algorithm>
#include<cstring>
#include<vector>
#define MAX 100
using namespace std;
int main()
{
void remove(char[]);
void add(char[], char);
char cstring[MAX];
char letter;
int ecount;
std::string str;
char selection;

cout << "Enter String: ";
cin.getline(cstring, MAX);
cout << "Size of String: " << strlen(cstring) << endl;

bool gameOn = true;
while (gameOn != false){
cout<<"\n Menu";
cout<<"\n========";
cout<<"\n A - Append";
cout<<"\n X - Exit";
cout<<"\n Enter selection: ";
cin>>selection;

switch(selection)
{
case 'A' :
case 'a' :
    cout << " Add Element: ";
    while (letter!='\n')
    {
    letter = cin.get();
    add(cstring, letter);
    }

    cout << "\n Output String: " << cstring;
    ecount = strlen(cstring) - 1;
    cout << " Size of String: " << ecount<< endl;
    break;
case 'X' :
case 'x' :{cout<<"\n To exit the menu";}
    break;
    default : cout<<"\n !!Invalid selection!!"<< endl;
    }
}
cout<<"\n";
return 0;
}


char * add( char *cstring, char c )
{
   int letter = strlen( cstring );

   if ( letter < MAX - 1 )
   {
      cstring[letter] = c;
      cstring[letter + 1] = '\0';
   }

   return ( cstring );
}

Answer 1

这是我疯狂的猜测。我认为你必须初始化letter。

使用以下代码检查它。是调试您正在切换的selection的值。

switch(selection)
{
case 'A' :
case 'a' :
    cout << "Add Element: ";

    letter = cin.get(); // this will initialize the char letter;

    while (letter != '\n') // or use ascii value of new line char in while condition 
    {
      add(cstring, letter); // first add it to string
      letter = cin.get(); // then get next letter  
    }

   cout << "String: " << cstring;
   ecount = strlen(cstring) - 1; // ecount must be a int
   cout << "Size of String: " << ecount<< endl;
break;

希望这会对你有所帮助

Answer 2

问题出在您正在阅读的输入中，当您在

中阅读字符时

cin>>selection;

它将读取一个字符并将其置于选择状态，当您按Enter键时，它将被存储在letter中，而您的循环将永远不会执行。

请参阅下面的代码，它工作正常;

#include<iostream>
#include <stdio.h>
#include <string.h>
#include<algorithm>
#include<cstring>
#include<vector>
#define MAX 100
using namespace std;
int main()
{
    void remove(char[]);
    void add(char[], char);
    char cstring[MAX];
    char letter;
    int ecount;
    std::string str;
    char selection;

    cout << "Enter String: ";
    cin.getline(cstring, MAX);
    cout << "Size of String: " << strlen(cstring) << endl;

    bool gameOn = true;
    while (gameOn != false){
        cout<<"\n Menu";
        cout<<"\n========";
        cout<<"\n A - Append";
        cout<<"\n X - Exit";
       cout<<"\n Enter selection: ";


       cin>>selection;
       cout<<"\n selection="<<selection;

       switch(selection)
       {
        case 'A' :
        case 'a' :
              selection=cin.get();
              cout << " Add Element: ";
              while (letter!='\n')
               {
                letter = cin.get();

                 add(cstring, letter);
               } 

               cout << "\n Output String: " << cstring;
               ecount = strlen(cstring) - 1;
               cout << " Size of String: " << ecount<< endl;
         break;
      case 'X' :
      case 'x' :cout<<"\n To exit the menu";
                gameOn=false;
      break;
      default : cout<<"\n !!Invalid selection!!"<< endl;
      } 
    }
    cout<<"\n";
    return 0;
   }

为什么在条件下切换不会执行

2 个答案: