Most control structures use a test expression that executes either selection (as in the: if then else) or iteration (as in the while; do while; or for loops) based on the truthfulness or falseness of the expression. Thus, we often talk about the Boolean expression that is controlling the structure. Within many programming languages, this expression must be a Boolean expression and is governed by a tight set of rules. However, in C++ every data type can be used as a Boolean expression because the value of any data type within C++ can be demoted into a Boolean value.

the concentration of capital and land in a few hands; overproduction and crises; it pointed out the inevitable ruin of the petty bourgeois and peasant, the misery of the proletariat, the anarchy in production, the crying inequalities in the distribution of wealth, the industrial war of extermination between nations, the dissolution of old moral bonds, of the old family relations, of the old nationalities.