C++ 邏輯運算符

#include <iostream> 
using namespace std; 
int main() 
{ 
     cout << "Do you wish to continue? <y/n> "; 
     char ch; 
     cin >> ch; 
     if (ch == "y" || ch == "Y")             // y or Y 
          cout << "You were warned!\a\a\n"; 
     else if (ch == "n" || ch == "N")        // n or N 
          cout << "A wise choice ... bye\n"; 
     else 
         cout << "else"; 
     return 0; 
} 

#include <iostream> 
const int SIZE = 6; 
using namespace std; 
int main() 
{ 
     float naaq[SIZE]; 
     int i = 0; 
     float temp; 
     cout << "First value: "; 
     cin >> temp; 
     while (i < SIZE && temp >= 0) // 2 quitting criteria 
     { 
         naaq[i] = temp; 
         ++i; 
         if (i < SIZE)             // room left in the array, 
          { 
              cout << "Next value: "; 
              cin >> temp;            // so get next value 
          } 
     } 
     return 0; 
} 

#include <iostream>
#include <climits>
using namespace std;
bool is_int(double); 
int main()
{
    
    double num;

    cout << "Enter an integer value: ";
    cin >> num;
    while (!is_int(num))    // continue while num is not int-able
    {
        cout << "Out of range -- please try again: ";
        cin >> num;
    }
    int val = int (num);    // type cast
    cout << "You"ve entered the integer " << val << "\nBye\n";
    return 0;
}

bool is_int(double x)
{
    if (x <= INT_MAX && x >= INT_MIN)   // use climits values
        return true;
    else
        return false; 
}

#include <iostream>
#include <cctype>              // prototypes for character functions
int main(){
    using namespace std;
    cout << "Enter text for analysis, and type @ to terminate input.\n";
    char ch; 
    int whitespace = 0;
    int digits = 0;
    int chars = 0;
    int punct = 0;
    int others = 0;

    cin.get(ch);                // get first character
    while (ch != "@")            // test for sentinel
    {
        if(isalpha(ch))         // is it an alphabetic character?
            chars++;
        else if(isspace(ch))    // is it a whitespace character?
            whitespace++;
        else if(isdigit(ch))    // is it a digit?
            digits++;
        else if(ispunct(ch))    // is it punctuation?
            punct++;
        else
            others++;
        cin.get(ch);            // get next character
    }
    cout << chars << " letters, "
         << whitespace << " whitespace, "
         << digits << " digits, "
         << punct << " punctuations, "
         << others << " others.\n";
    return 0; 
}