Module 4- Flow Control

Module 4: Flow Control By SRIRAM . B

Overview 

Statement 

Selection – if, switch



Iteration



Jump

- while, do..while, for, foreach - break, continue, goto, return

Statements 

Statements are the smallest unit of execution in C# programs. They can be grouped into sequences using curly braces. These are called Compound Statements or Blocks. A compound statement can be used in place of simple statement.



C# provides variety of statements. Most of the statements are similar to C,C++,Java.



The statements in C# can be categorized as: 

Selection Statements



Iteration Statements



Jump Statements

Selection Statements 

Selection Statements selects one of a number of possible statements for execution based on the value of a controlling expression.



A selection statement can be:

If Statement



Switch Statement

If Statement 

The If statement selects a statement for execution based on the value of a Boolean expression.

Syntax:If(condition 1) statement_1 Else statement_2 statement_3 The condition is tested first. If the condition evaluates to TRUE then statement_1 is executed otherwise statement_2 is executed. After that statement_3 is executed.

Example 1 – If Statements using System; class If_construct { public static void Main() { int var1 =10; if (var1 > 0) Console.WriteLine(“Your number is greater than 0"); else Console.WriteLine(“Your number is less than or equal to 0”); } }

Example 1 – If Statements.. Output of the code is: Your number is greater than 0

Nested If 

The If statement may be nested to many levels. This means If statement may contain another If statement.



Syntax:If(condition 1) If(condition 2) statement_1 Else statement_2

Example – Using Logical Operators in If..else Check the age of an applicant and display an appropriate message as follows: Print the message “ Valid age” if the age of the candidate is between 18 and 25 and print “Invalid age” if the age criterion is not satisfied. using System; class IF { public static void Main() { int age=26; if (age >=18 && age <=25)

Example – Using Logical Operators in If..else .. Console.WriteLine("Valid age"); else Console.WriteLine("Invalid age"); } } Output of the code is: Invalid age

Example 1 – Nested IF using System; class NestedIF { public static void Main() { int A=30;int B=50;int c=25; if (A > B) { if (A > C) { than” +C

Console.WriteLine(A+ “is greater + “and” +B);

}

Example 1 – Nested IF.. else if (A > C) { Console.WriteLine(B+ “is greater than” +C + “and” +A); } } }

Switch Statement  A switch…case statement executes the statements that are associated with the value of controlling expression as follows:  The switch expression is evaluated first and acts as the control of execution.  If the value of the case label matches the switch expression, then the statements following it are executed.  A label in a case is a fixed value.  If no label matches the value of the switch expression, then the statements following the default label are executed.

Switch Statement Syntax 

Syntax:-

switch(expression) { case : Statements case : Statements default: Statements }

Example – Switch Case Statement using System; class Switch_case { public static void Main() { int i=12; switch(i) { case 12: Console.WriteLine(“Dozen"); break;

Example – Switch Case Statement .. case 20: Console.WriteLine(“Score"); break; default: Console.WriteLine("default"); break; } } } Output of the code is: Dozen

Iteration Statements 

While Statement



Do..While Statement



For Statement



Foreach Statement

Iteration Statements 

Iteration constructs are also known as loop constructs.



Loop constructs are used for the repeated execution of statements based on a given condition.



The condition has to be an expression that returns a Boolean value.



The execution of the statements within a loop continues as long as a condition is true.



When the condition specified in the loop evaluates to false, control is transferred to the statement following the loop.



Some of the iteration constructs are: 

while



do…while



for



foreach

Diff. Between While & Do..While Statements While 



Condition is tested at the beginning of the loop Loop will execute once the condition is true

Do..While 

Condition is tested at the end of the loop



Loop will execute at least once even the condition is false

While Statement 

The while statement is used to conditionally execute a set of statements zero or more times. A while statement can be executed as follows:

The boolean expression is evaluated



If the boolean expression is true, the control is transferred to statements, once it reaches the end point of the statement the control is transferred to the beginning of the while statement.



If the boolean expression is false, controls is transferred to the end point of while statement



Syntax:while(condition) { }

statement;

Example 1 : While Statement using System; class While_construct { public static void Main() { int i=0; //Initialization while (i<3) //Condition { Console.WriteLine(i); //Loop body i++; //Re-initialization } } }

Example 1 : While Statement Output Output of the code is: 0 1 2

Do..While Statement 

The do..while statement conditionally executes an statement one or more times. A do..while statement is executes as follows:

Control is transferred to statement



When the control reaches the end point of the statement, the condition is evaluated. If the boolean expression is true, the control is transferred to begin of the do..while loop, otherwise the control is transferred to the end point of the do..while statement.



Syntax:do { statement; }while(condition)

Example : Do..While Statement using System; class Do_while { public static void Main() { int i=3; //Initialization do { Console.WriteLine(i); //Loop body i++; //Re-initialization }while(i<3);//Condition } }

Example : Do..While Statement Output Output of the code is: 3

For Statement 

The for statement consists of the keyword, for, followed by parenthesis which contains three expressions that are separated by a semicolon.



The expression consists of the initialization expression, the condition and the re-initialization expression.



The general structure of a for construct is for(initialization; condition;re-initialization) { Statements }

Example – For Statement using System; class For_construct { public static void Main() { for(int i=0;i<3;i++) { Console.WriteLine(i); } } }

Foreach Statement 

Repeats a group of statements for each element in an array or an object collection.



Syntax :foreach( type variable in list) { statements }



Example foreach(int I in arr) { statements }

Example - Foreach Statement using System; class Foreach { public static void Main() { int[]arr = new int {0,1,2,5}; foreach(int i in arr) { Console.WriteLine(“Element is {0}”, i); } } }

Jump Statements 

Break Statement



Continue Statement



Goto Statement



Return Statement

Jump Statements 

Jump statements are used to unconditionally transfer control to program statements.



The location to which a jump statement transfers control is referred to as the target.



When a jump statement transfers control to a statement outside the block, it exits the block.

Jump Statements.. Some of the jump statements are : 

The break statement is used to terminate a case in a switch statement and terminate a loop, bypassing the loop condition.



The continue statement forces the next iteration of the loop to take place, skipping any code following the continue statement in the loop body.



The goto statement is used to transfer control to a statement that is marked by a label.



The return statement is used to return control to the caller function in which the return statement is used.

Example 1 - Break Statement using System; class Hello { public static void Main() { int i=1; do {

Console.WriteLine(i); if(i==5) break;

}

}

i++; }while (i<100);

Example 1 - Continue Statement using System; class Hello { public static void Main() { for (int var = 1; var <= 10; var++) { if (var < 9) continue; Console.WriteLine(var); } } }

Example - Goto Statement using System; class Hello { public static void Main() { for (int var = 1; var <= 10; var++) { if (var < 9) goto finish; Console.WriteLine(var); } finish: Console.WriteLine("After finish"); } }

Example - Return Statement

Exercise What is the difference between while and do… while construct? What is the purpose of the break statement? Predict the output of the following code using System; class Hello { public static void Main() { int var; for (var = 1; var <= 10; var++); { Console.WriteLine(var); } } }

Exercise.. Write a program to generate the first twenty numbers in a Fibonacci series – 0 1 1 2 3 5 8 13 …. Write a program to print all even numbers from 1 to 100. Write a program that displays the count of numbers which are divisible by 5 in the range 1 to 100.

Flow Control Flashback 

Statement 

Selection – if, switch



Iteration



Jump

- while, do..while, for, foreach - break, continue, goto, return

Session Ends

Exercise

Relax