Generally a program executes its statements from beginning to end. But not many programs executes all their statements in strict order from beginning to end. Most programs decide what to do in response to changing circumstances. These programs not only store data but they also manipulate data in terms of consolidation, rearranging, modifying data.
To perform their manipulative miracles, programs need tools for performing repetitive statements to attain so. Such statements are called program control statements.
In a program, statement may be executed sequentially, selectively or iteratively. Every programming language provides constructs to support sequence, selection or iteration. Let's discuss what is means by sequence, selection or iteration constructs.
The sequence construct means the statements are being executed sequentially. This represent the default flow of control. Every C++ program begins with the first statement of main(). Each statement in turn is executed (sequence construct). When the final statement of main() is executed, the program is done. This construct specifies the normal flow of control in a program and is the simplest one.
Note - In C++, the program execution starts with the first statement of main() and ends with the last statement of main(). Therefore, the main() is also called driver function as it drives the program.
The selection construct means the execution of statement(s) depending upon a condition-test. If a condition evaluates to true, a course-of-action (a set of statements) is followed otherwise another course-of-action (a different set of statements) if followed. This construct (selection construct) is also called decision construct because it helps in making decision about which set-of-statements is to be executed. You will learn in detail about this topic in the following two separate chapters:
The iteration construct means repetition of a set-of-statements depending upon a condition-text. Till the time a condition is true (or false depending upon the loop), a set-of-statements are repeated again and again. As soon as the condition becomes false (or true), the repetition stops. The iteration construct is also called looping construct.
The set-of-statements that are repeated again and again is called as body of the loop. The condition on which the execution or exit of the loop depends is called the exit condition or test-condition. You will learn in detail about this topic in the following two separate chapters: