The first sub-statement of an if statement may be followed by the keyword else. The sub-statement after the else keyword will be executed when the condition is false (that is, when the first sub-statement is not executed).

int x;
std::cin >> x;
if (x % 2 == 0) {
    std::cout << "The number is even\\n";
} else {
    std::cout << "The number is odd\\n";
}