Why isn't this working (C++)?

[Catch_22]

I'm trying to write a program that repeatedly asks for characters until "$" is entered. The program then outputs the number of characters entered before the $ was entered.

So I did this:

#include <iostream>
using namespace std;

int main() {


int b;
char a;

b = 0;

do{ cout << "Enter character: ";
cin >> a;
b++;
} while ( a != "$" );

cout << b << "\n";

return 0;

}

I called this "dollar.cpp".

Unfortunately, the program doesn't compile. I get this as an error:


dollar.cpp:23:20: warning: comparison with string literal results in unspecified behaviour
dollar.cpp:23:20: error: ISO C++ forbids comparison between pointer and integer

What's wrong here?

[Rubberman]

Try single quotes around the dollar sign in the while() condition. IE:

} while (a != '$');

This is a pretty common sort of mistake for beginning programmers.

[Catch_22]

Thanks, it works!!

Can I just ask, what is the difference between " and '?

When i'm using cout, i'm using " so what's the general rule for using one or the other?

[elija]

Single quotes are for a character and double quotes are for a string, which more accurately would be a pointer to a string.

[Rubberman]

Thanks, it works!!

Can I just ask, what is the difference between " and '?

When i'm using cout, i'm using " so what's the general rule for using one or the other?

What elija said. This may clarify the "rule":

char stuff[] = { 'a', 'b', 'c', 0 }; // an initialized string/char array variable.
char a = stuff[0];
char b = stuff[1];
char c = stuff[2];
char* astring = stuff; // Or, char* astring = &stuff[0]; - same thing.

if (a == 'a') printf("ok, a == 'a'\n");
if (b != 'b') printf("not ok - b != 'b' should not compute since b (stuff[1]) == 'b'\n");
if (c == "c") printf("not ok - c is not a string, it's a char\n"); // This would cause your compiler error.
if (astring == stuff) printf("ok - astring points to stuff\n");
if (astring == "abc") printf("not ok - astring (alias stuff) has same data, but not same address as \"abc\" string literal\n");
if (strcmp(astring, "abc") == 0) printf("ok - astring contains same data as \"abc\" string literal\n");

Are we confused yet?