Solution

Definition
A C++ program is a set of instructions of the C++ programming language that can be interpreted by a computer into a sequence of basic operations that the computer can perform.

Axiom
A C++ program consists of a set of global declarations/definitions and several nested groups of instructions. Each group of instructions is delimited by curly brackets ({ }).

Definition
The rank of a group of instructions in a C++ program is the nesting level of the group in the program. Global declarations/definitions are defined to be at rank 0.

Definition
Consider a C++ program with instructions $I_1,\ldots,I_n$ . For a given $K>0$ , a group of $t$ instructions $(I_h,\ldots,I_{h+t})$ at rank $r$ in a C++ program is well-$K$ -indented if:

1. no two instructions are on the same line of text;
2. the opening curly bracket is on a line of text above $I_h$ and the closing curly bracket is on a line of text below $I_{h+t}$ ;
3. $I_{h-1}$ (the last instruction at rank $r-1$ before the beginning of the group) starts $K$ columns of text before $I_h$ ;
4. the closing curly brace of the group is aligned with instruction $I_{h-1}$ (in other words, it is positioned $K$ columns of text before $I_{h+t}$ ).

Definition
A C++ program is well-indented if there is an integer $K>0$ such that (a) the global declarations/definitions start at column 0, and (b) each of its instruction groups is well-$K$ -indented.

Fact
Usual values for $K$ are 2, 4, 8. In this course, the value $K=2$ is favoured as it allows for a greater number of nesting levels to be displayed in 80 characters (the usual screen width on UNIX systems).