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Up until this point, you have seen that conditional statements may be either:

• a Boolean-valued variable, e.g., if ( found ) {...,
• a Boolean-valued operator ==, !=, >=, >, <= and <, or
• logical operators &&, || and !, the arguments of which are Boolean-valued values, Boolean-valued operators or logical operators.

Now, try the following:

#include <iostream>

int main();

int main() {
	for ( int i = 10; i; --i ) {
		std::cout << i << std::endl;
	}

	return 0;
}

First, i is not a conditional statement, it is simply a variable, so how does this work?

C++ is extremely lax in its interpretation of true and false:

• If the conditional statement is integer-valued, then 0 is interpreted as false, and all other non-zero values are interpreted as true.
• If the conditional statement is real-valued, then 0 and -0 are interpreted as false and all other real values are (including inf and nan) are interpreted as true.
• If the conditional statement is an address, the null pointer (nullptr) is interpreted as false and all other addresses are interpreted as true.

From a programming point of view, however, the conditional statement

	if ( x ) {
		// do something...
	}

can always be converted to a Boolean-valued operator with one of

	if ( x != 0 ) {	            // if 'x' is an integer type
	if ( x != 0.0 ) {	    // if 'x' is a real type
	if ( x != nullptr ) {	    // if 'x' is an address

You may object: "But this is one more operator, and therefore slower!" If your compiler does not produce exactly the same output with the following two pieces of code:

// Program 1
#include <iostream>

int main();

int main() {
	double n;
	double x;

	std::cout << "Enter an integer: ";
	std::cin >> n;

	if ( n != 0 ) {
		std::cout << "It is non-zero" << std::endl;
	} else {
		std::cout << "It is zero" << std::endl;
	}

	std::cout << "Enter a real number: ";
	std::cin >> x;

	if ( x != 0.0 ) {
		std::cout << "It is non-zero" << std::endl;
	} else {
		std::cout << "It is zero" << std::endl;
	}

	return 0;
}

// Program 2
#include <iostream>

int main();

int main() {
	double n;
	double x;

	std::cout << "Enter an integer: ";
	std::cin >> n;

	if ( n ) {
		std::cout << "It is non-zero" << std::endl;
	} else {
		std::cout << "It is zero" << std::endl;
	}

	std::cout << "Enter a real number: ";
	std::cin >> x;

	if ( x ) {
		std::cout << "It is non-zero" << std::endl;
	} else {
		std::cout << "It is zero" << std::endl;
	}

	return 0;
}

then the onus is on you to get a real compiler.

For the same reason that Java bans the automatic conversion of either integer values, real values or addresses, it is in your best interest to do so, as well: it is much less likely that a programmer will misinterpret a conditional statement and cause a subsequent error.

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