Logical AND and OR operators: short-circuit evaluation

From C++ Primer:

The logical AND and OR operators always evaluate their left operand before the right. The right operand is evaluated only if the left operand does not determine the result. This evaluation strategy is often referred to as "short-circuit evaluation."

 

A valuable use of the logical AND operator is to have expr1 evaluate to false in the presence of a boundary condition that would make the evaluation of expr2 dangerous. As an example, we might have a string that contains the characters in a sentence and we might want to make the first word in the sentence all uppercase. We could do so as follows:

     string s("Expressions in C++ are composed...");

string::iterator it = s.begin();

// convert first word in s to uppercase

while (it != s.end() && !isspace(*it)) {

*it = toupper(*it); // toupper covered in section 3.2.4 (p. 88)

++it;

}