Use Of ||(OR) In While Loop___What Should Be The Right Code

[noobcoder9867]

So I Have Written A Code That Should Accept A Specific Words Only, but The while Loop Is Not Working
What's Wrong In This Code

#include<iostream>
#include<string.h>
using namespace std;

int main()
{
    char class_name[20];
    cin>>class_name;
        while((strcmp(class_name,"Business")==1) || (strcmp(class_name,"business")==1) || (strcmp(class_name,"Economy")==1) || (strcmp(class_name,"economy")==1) || (strcmp(class_name,"public")==1) || (strcmp(class_name,"Public")==1))
        {
            cout<<"Error!! Invalid Input(Plz Enter Business,Public,Economy Only)";
            cout<<"\nRe-Enter Class:";
            cin>>class_name;
        }
}

[Repeater]

For starters, strcmp returns 0 if the words are the same. You're comparing against 1, which means they're different in a very particular way. The could be different and the number is -1. They could be different and the number is 17; it's implementation defined.

But even using strcmp here is not good. If you're going to write C++, then write C++.

#include<iostream>
#include<string>
using namespace std;

int main()
{
    string class_name;
    cin>>class_name;
        while(class_name != "Business" && 
              class_name != "business" &&
              class_name != "Economy" &&
              class_name != "economy" &&
              class_name != "Public" &&
              class_name != "public")
              {
                cout<<"Error!! Invalid Input(Plz Enter Business,Public,Economy Only)";
                cout<<"\nRe-Enter Class:";
                cin>>class_name;
              }
}

[jlb]

Why are you using C-strings instead of C++ strings? Comparison of C++ strings is much easier.

If you must use C-strings you probably should look up your documentation for strcmp(), it doesn't return 1 for a match.

You may also want to consider transforming the class_name to a single case, then you would only need to check for one option.

[jonnin]

and a general design thing: making a user type that much is 'unfriendly'. Put a menu on it and let them type a single digit or letter to select from the valid list. Its easier for both you and the user to do it this way: all they can mess up is a single letter, which can be covered in a default switch statement.

[Ganado]

#include <iostream>
#include <string>
#include <map>
#include <algorithm>
#include <cctype>
using std::string;
using std::map;
using std::cout;
using std::cin;

class SchoolClass {
  public:
    int num_credits;
};

std::string tolower(std::string str)
{
    // https://stackoverflow.com/a/313990/8690169
    std::transform(str.begin(), str.end(), str.begin(),
        [](unsigned char c){ return std::tolower(c); });
    return str;
}

int main()
{
    map<string, SchoolClass> class_map = {
        { "business", SchoolClass{1} },
        { "economy", SchoolClass{4} },
        { "public", SchoolClass{3} }
    };
    
    cout << "Enter Business, Public, or Economy: ";
    string class_name;
    cin >> class_name;
    class_name = tolower(class_name);
    
    auto it = class_map.find(class_name);
    while (it == class_map.end())
    {
        cout << "Error!! Invalid Input(Plz Enter Business,Public,Economy Only)\n";
        cout << "Re-Enter Class: ";
        cin >> class_name;
        class_name = tolower(class_name);
        it = class_map.find(class_name);
    }
    
    cout << "Number of credits: " << it->second.num_credits << '\n';
}