How to make the 'switch' function hold 2 characters?

[Tiger58]

There is this problem I am trying to do, the instructor asked us to do in both "if" and "switch" ways, the "if" was easy but how exactly do you make a switch hold something other than an integer or single character??

Write a program that asks the user to enter one of the following state abbreviations: NC, SC, GA, FL, or AL. the program should then display the name of the state that corresponds with abbreviation entered (North Carolina, South Carolina, Georgia, Florida, or Alabama).

Input Validation: Accept abbreviations with both letters in uppercase or both in lower case. Display an error message if an abbreviation other than one of these five is entered.


This is what I got so far, and obviously it doesn't seem to work:

#include <iostream>
using namespace std;

int main()
{
char state[2];

cout<<"Enter the state abbreviation: ";
cin.get(state,2);

switch(state)
{
case "NC":
case "nc": cout<<"North Carolina";
break;

case "SC":
case "sc": cout<<"South Carolina";
break;

case "GA":
case "ga": cout<<"Georgia";
break;

case "FL":
case "fl": cout<<"Florida";
break;

case "AL":
case "al": cout<<"Alabama";
break;

default: cout<<"You have entered an invalid abbreviation.";
}

cin.get();
return 0;
}

Is there any way I can modify this so it can go through?

[ssrun]

Switch case statments can only have cases that represent a single integer or character.

If you look closely, each state is uniquely specified by its first letter. I think that's why your prof chose those specific abbreviations.

[Tiger58]

But it also says to display the default message if any other abbreviation is entered, such as one from another state. How would it distinguish between AL and AR?

[striker24]

will it be okay if i post a different set of codes? i'll try to create a running program but i am working it in dev c++ compiler. will it be fine?

[Tiger58]

Sure, I just want to see how such a program would work

Edit: Yea the if/else was simple to do with this problem, just trying to figure out how to do this switch one. Is there a way to use the AND logical operator within a case?

[striker24]

ok. because i am more familiar in using if-else statement..

[JLBorges]

This is one way to do it:

std::string state ;
std::cout << "state? " && std::cin >> state ;
if( state.size() != 2 ) { /* error */ }

state[0] = std::toupper( state[0] ) ;
state[1] = std::toupper( state[1] ) ;

// assumes that the max value that a char can hold is less than 10000
enum { MULTIPLIER = 10000 } ; 
const long long key = state[0] * MULTIPLIER + state[1] ;

switch(key)
{
     case 'N' * MULTIPLIER + 'C' : /* North Carolina */ break ;
     case 'S' * MULTIPLIER + 'C' : /* South Carolina */ break ;
     // etc ...
     default : /* error */
}

[Tiger58]

I'm always seeing those : : things and other terms such as "std" (I have only used std in the namespace) I that I am clueless about. Are there different ways of learning C++ or why is it I haven't even seen any : : in my book so far? Is it an older style?

Also, I'd use that code but I don't understand half of it

[ssrun]

You can nest the switch case statements for simplicity. First check the case for N then if it's true check if the second letter is C by using another switch statement inside the N case if not print an error. It's more long winded but I think that might be the point of the assignment. To compare and contrast if vs switch statements depending on what you want to check.

[Tiger58]

Doesn't seem to be working, tried nesting the case of 'N' with another switch that had the case 'C' and nothing

[JLBorges]

> I'm always seeing those : : things and other terms such as "std" ...
> ... why is it I haven't even seen any : : in my book so far?

Your book may be dumping a using namespace std ; right t the top of every code snippet.

There was a recent discussion here about the pros and cons of doing that:
http://www.cplusplus.com/forum/general/72248/


> I'd use that code but I don't understand half of it

Once you realize that std::cin or std::toupper() can be written as just cin or toupper() with a using directive in place, you should be able to figure out how a unique integer key is made for each two character sequence.

[Tiger58]

Seems to work, if you don't mind though, would you explain what these lines are actually doing?

enum { MULTIPLIER = 10000 } ;
const long long key = state[0] * MULTIPLIER + state[1] ;

And what is the toupper function for? And why did you put a 0 and 1 in brackets there?

[JLBorges]

> would you explain what these lines are actually doing?
>

enum { MULTIPLIER = 10000 } ; 
const long long key = state[0] * MULTIPLIER + state[1] ;

> And why did you put a 0 and 1 in brackets there?

state[0] is the first char in the string, the one at at position 0,
state[1] is the second char in the string, the one at at position 1.

if the string state holds "AB", state[0] is 'A' and state[1] is 'B'
Assuming that 'A' has a value of 65, and 'B' has a value of 66,
state[0] * MULTIPLIER + state[1] is 65 * 1000 + 66, or 65066

> And what is the toupper function for

http://en.cppreference.com/w/cpp/string/byte/toupper
We just convert each lower case character in the input to upper case first.

[ssrun]

switch (state[0]) {
case 'N':
case 'n':
        switch (state[1]) {
        case 'C':
        case 'c':
                 cout << "North Carolina" << endl;
                 break;

        default:
                  cout << "Invalid state" << endl;
                  break;
        }
        break;

// other cases

default:
     cout << "Invalid State" << endl;
     break;
}

[Mathhead200]

BTW, the reason a switch doesn't work for this is (basically) the same reason that you can't compare C-strings with the == operator, (although that will at least compile.)

Here's an example of what I mean, along with some output from a run on my machine; (the output will be machine and runtime specific):

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

#include <cstring> #include <iostream> using namespace std; /** * Invoke the program like this: * %>program_name.exe Test * * argc: the number of arguments passed into the program + 1 * argv: the value of those arguments (starting at index 1) */ int main(int argc, char *argv[]) { //check that there is an argument if( argc <= 1 ) { cerr << "Please supply an argument.\n"; return 1; } //doesn't even compile /* switch( argv[1] ) { case "Test": cout << "Yea!\n"; break; default: cout << "Nea!\n"; } */ //doesn't work like you might expect if( argv[1] == "Test" ) cout << "Yea!\n"; else cout << "Nea!\n"; //this is why cout << (void*)"Test" << endl; cout << (void*)argv[1] << endl; //one way you could do it correctly if( strcmp(argv[1], "Test") == 0 ) cout << "Yea!\n"; else cout << "Nea!\n"; return 0; }

Nea! 000000013FB9D394 00000000004B38AE Yea!