Introduction to C/C++ Lecture 3 - Program Flow Control · Introduction to C/C++ Lecture 3 - Program...

Introduction to C/C++Lecture 3 - Program Flow Control

Rohit SehgalNishit Majithia

Association of Computing Activities,Indian Institute of Technology,Kanpur

[email protected]@cse.iitk.ac.in

May 25, 2016

Rohit Sehgal Nishit Majithia (IITK) ACA May 25, 2016 1 / 22

Fruits for some may seem poison to Others.


Conditionals and Loops

This topic focuses on:

Boolean expressions

conditional statements

repetition statements

iterators


Control Flow

Until specified, the execution of the statements is LINEAR: One byOne

Some conditional statements gives power to:

Execute particular statement or notExecute a statement repetitively

These decisions are based on the Boolean Expression


Conditional Statements

There are mainly 3 conditional statements provided in C/C++

if statements

if-else statements

switch statements


IF Statements

Syntax

if ( condition )statement;

if : C/C++ keyword

condition: The condition must be a boolean expression

statement: If the condition is true, the statement will be executed


Boolean Expressions

Expression Meaning

= = equal to!= not equal to< less than> greater than<= less than or equal to>= greater than or equal to


Logical Operators

Logical NOT

!a

If a is true, then !a is false and vice-versa

Logical AND

a && b

If a is true and b is also true, then a && b is true otherwise false

Logical OR

a || b

If a is false and b is also false, then a || b is false otherwise true


If-else Statements

Syntax

if ( condition )statement 1;

elsestatement 2;

if,else: C/C++ keyword

condition: The condition must be a boolean expression

statement: If the condition is true, the statement 1 will be executedotherwise statement 2 will be executed.


Contd...

Nested if-else

else-if ladder


switch Statements

Syntax

switch ( expression ){

case value1 :statement1;

case value2 :statement2;

case ...}

switch,case: C/C++ keyword

If expression matches with any value, then corresponding statementwill be executed

Often a break statement is used as the last statement in each case’sstatement list


Compound Assignment

C provides compound assignment operators which enable a moreconcise notation

temp = temp + 1 is same as temp += 1

temp = temp - 1 is same as temp -= 1

temp = temp * 1 is same as temp *= 1

temp = temp / 1 is same as temp /= 1


Increment and Decrement Operators

The increment (i.e., ++) or decrement (i.e., - -) operators are thefrequently used operators which take only one operand.

The ++ operator is same as the compound assignment withIncrement of 1 and the - - operator is same as the compoundassignment with Decrement of 1

Prefix Increment/Decrement

j = ++i;Increment i and then use it

Postfix Increment/Decrement

j = i++;Use i and then increment it


Precedence of operators

Table: Precedence order from higher to lower

Operators Associativity

() [] -> . left to right

! ++ - - right to left

* / % left to right

+ - left to right

< <= > >= left to right

== != left to right

&& left to right

|| left to right

= += -= *= /= %= right to left


Loops

Loop is a control structure that repeats a group of steps in a program.

There are mainly 3 C/C++ loop control statements:

for statementwhile statementdo-while statement


for statement in C/C++

Syntax

for ( expr1 ; expr2 ; expr3 ){

statement-list;}

expr1 is used to initialize the loop.

expr2 is a logical expression controlling the iteration. The loop exitswhen expr2 becomes false.

expr3 typically modifies a variable in expr2 eventually causing expr2to become false.

Any or all of the expressions in a for statement can be missing, butthe two semicolons must remain.


Contd ...

One can use the comma operator in a for statement to do:

Multiple Initialization

for ( expr1 , expr2 ; expr3 ; expr4 )

Here expr1 and expr2 will initialize at the same time


Contd ...

One can use the comma operator in a for statement to do:

Multiple InitializationMultiple processing of indices

for ( expr1 , expr2 ; expr3 ; expr4 , expr5 )

Here expr4 and expr5 will process the initialized expr1 and expr2 atthe same time


while statement in C/C++

Syntax

while ( expr ){

statement-list;}

First expr is evaluated. If it is true, then statement-list is executed,and control is passed back to the beginning of the while loop.

Any for loop can be converted into while loop and vice-versa.


do-while statement in C/C++

Syntax

do{

statement-list;} while ( expr );

statement-list will first executed and then check the expr, if it is truethen loop continues.

The do statement is a variant of the while statement that tests itscondition at the bottom of the loop.


goto statement in C/C++

goto causes an unconditional jump to a labeled statementsomewhere in the current function.

Syntax

label: goto label;... ...

goto label; label:... ...

goto can make a program very difficult to read and understand. It isnever needed.


The End


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