a string switch statement in c++

pengu · 02-24-2006, 11:04 AM

hi, I am trying to make a switch statement using a string. I can do the same thing with a long if-else statement but it would be less efficient. Here is my code.

Code:

int main() //find out what shape needs solvig
{
	string e;   //when to exit (see while loop)
	string choice; // help, shapes, or 'figure'
	string shapes; //list shapes implemented by this program
	shapes = "rectangle";
	
	e = "n";
	while (e == "n")
	{
		title();

		cout << "Typeing \"help\" will give help"               << endl; //options...
		cout << "Entering a shape name will jump to that shape" << endl;
		cout << "Typing \"shapes\" will list included shapes"   << endl;
		
		cout << "Selection: "; //selected option
		getline(cin, choice);
		
		switch(choice)
		{

			case "help"              : help(); break;
		
			case "shapes"            : cout << shapes; break;
		
			case "circle"            : circle(); break;
		
			case "triangle"          : triangle(); break;
		
			case "rectangle"         : rectangle(); break;
		
			case "sphere"            : sphere(); break;
		
			case "rectangular prism" : recprism(); break;
		
			case "triangular prism"  : triprism(); break;
		
			case "pyramid"           : pyramid(); break;
		
			case "cone"              : cone(); break;
		
			default                 : cout << choice << " not yet implemented"; break;
		}
		
		cout << "\nDo you want to exit? y/n ";
		getline(cin, e);
	}
	return 0;
}

this fails to compile with the simple error

Code:

c.cpp: In function ‘int main()’:
c.cpp:37: error: switch quantity not an integer

is there any way to make this work?
thx in advance

swodniw · 02-24-2006, 11:33 AM

Quote:

this fails to compile with the simple error

Code:

c.cpp: In function ‘int main()’:
c.cpp:37: error: switch quantity not an integer

The clue here is the error message. You can not switch on a string.

I thought it was apt that I answered this question when you sign says

Quote:

... windows cd backwords ...

pengu · 02-24-2006, 11:40 AM

thx for the fast reply, but i was wondering if there was a way to make it work... my dad used to program c and he said there was a way but he couldnt remember how.

swodniw · 02-24-2006, 11:43 AM

Quote:

Originally Posted by pengu

thx for the fast reply, but i was wondering if there was a way to make it work... my dad used to program c and he said there was a way but he couldnt remember how.

Lol tell your dad he is wrong. For a start C doesn't have strings it uses arrays. For a quick fix ask the user to enter an int.
ie 0 to exit
1 to display...

pengu · 02-24-2006, 11:51 AM

ok, if your sure...

i cant use an int because i want the user to enter a shape, (like "rectangle") and the program will jump to that function.

i suppose i will just use an if-else block then. unless there is a way to cast a string into a int.

sorry for my newbeiness... i'm learning my first programming language with "C++ programming in easy steps" as my only recource.

michaelk · 02-24-2006, 11:53 AM

You can use char but not string.
Is this homework?

pengu · 02-24-2006, 12:15 PM

Quote:

Originally Posted by michaelk

You can use char but not string.

is there any way to use a char array or vector

Quote:

Originally Posted by michaelk

Is this homework?

um... no.... i just said i'm self taught.

paulsm4 · 02-24-2006, 01:14 PM

1. You answered your own question in your first post: a C/C++ "switch/case" block only works with "int" types. If you want something that looks like a "switch/case" block and still uses strings (aka "C char[] arrays"), then you get to use a bunch of "strcmp()'s" in a block of "if/then/else" statements. Period.

2. An alternative, however, might be to forget about the "switch/case" block concept, and use an STL map instead.

Just a thought .. PSM

michaelk · 02-24-2006, 01:20 PM

http://www.phim.unibe.ch/comp_doc/c_...AX/switch.html
Console menu systems typically use a single number (0-9) or a single character and not a whole word. I did a quick search and found a couple of examples.

http://www.java2s.com/ExampleCode/De...uselection.htm
http://code.dreamincode.net/snippet41.htm

Vagrant · 02-24-2006, 03:58 PM

You can switch on a single char, which is an integer type, maybe that's what your dad meant. You have your user just input a character representing the choice. This is the simplest method both for you and your users.

pengu · 02-24-2006, 04:02 PM

ok, thx for the help. ill just use if then statements

Vagrant · 02-24-2006, 04:05 PM

Ok, but if you just use a char representation then the user doesn't have to type out each shape, its cumbersome and easy to mess up. My thoughts.

Ictus · 02-24-2006, 06:03 PM

There's a possibility to use switch with strings. But i wonder if it's worth the work. ^_^

You can create your own String-class (inherited from std::string) and override the static_cast operator for int:

class mystring : std::string
{
// ...
public
operator int() { ... };
};

Within that overriden operator you can try to generate a unique integer for each string, for example with the CRC32 algorithm.
When using that string class in the switch statement u can easily use the normal strings, but actually it only works with the integer values.

That's the only possibility that comes into my mind right now.

ta0kira · 02-25-2006, 05:51 PM

The easiest way is to break it down like the compiler would on its own:

Code:

if (choice == "help")                   help();

else if (choice == "shapes")            cout << shapes;
		
else if (choice == "circle")            circle();
		
else if (choice == "triangle")          triangle();
		
else if (choice == "rectangle")         rectangle();
		
else if (choice == "sphere")            sphere();

else if (choice == "rectangular prism") recprism();

else if (choice == "triangular prism")  triprism();

else if (choice == "pyramid")           pyramid();

else if (choice == "cone")              cone();

else cout << choice << " not yet implemented";

'switch' will only work with integral data types, AFAIK.
ta0kira

xhi · 02-25-2006, 09:58 PM

a common thing to do would be to make a numbered menu,.

ex..
1. Square
2. Triangle
3. Circle
etc..

the user will enter a number and then you can use a switch on the number selection..

you can use an enum or defines if you want to code to be more readable..