BASIC CONTROL STRUCTURE

• Control structures are the basic entities of a structured programming language
• The mechanism that allow us to control the flow of execution are called control structures. 
• There are 4 main categories of control structures :
• Sequence
• Selection
• Iteration
• Branching

SEQUENCE

    

• Do one instruction the the next and the next
• It just executes them in the given sequence or in order listed
• Most lines of the code in the program belongs to this category.

e.g :

statement 1 is executed first, followed by statement 2, then finally statement 3.

SELECTION

    
• Selection structures are used to perform ‘decision making‘ and then branch the program flow based on the outcome of decision making
• Implemented in C/C++ with If, If Else and Switch statements
• If and If Else statements are 2 way branching statements 
• Switch is a multi branching statement.

e.g : If - then - else

if (condition) then

   Statement 1;

else

   Statement 2;

• Condition is a boolean expression 
• Evaluates either True / False
• If True - Statement 1 will be executed
• Otherwise - Statement 2 will be executed
• S1 & S2 may be single statement or group of statements

ITERATION

• Iterative construct means that some statements will be executed multiple times until some condition is met
• Such construct implements a loop structure in which action is executed multiple times, as long as some condition is true 
• In C, iterative constructs can be implemented using while, do-while, or for loop statements
• While is an entry controlled loop. Statement inside braces are allowed to execute only if condition inside while is TRUE.
• Do while is an exit controlled loop.
• For statement is an entry controlled loop. 
• The difference between while and for is in the number of repetitions.
• The for loop is used when an action is to be executed for a predefined number of times. 
• The while loop is used when the number of repetitions is not predefined.

e.g :

BRANCHING

• A control structure that allows the flow execution to jump to a different part of the program.
• This category is rarely used in modular structured programming.

e.g : Go - To Statement

• It provides an unconditional jump from the 'goto' to a labelled statement in the same function.
• Use of go-to statement is highly discouraged in any programming language because it makes difficult to trace the control flow of a program, making the program hard to understand and hard to modify. 
• Any program that uses a go-to can be rewritten to avoid them.