Fcp chapter 2 upto_if_else (2)

Control Instruction
alter our actions by circumstances.
If the weather is fine, then I will go for a stroll
If the highway is busy I would take a diversion
notice that all these decisions depend on some condition being
met
C language too must be able to perform different sets of
actions depending on the circumstances
C has three major decision making instructions
If statement
if-else statement
SThe conditional operators.
switch statement

Decisions! Decisions!
Last class programs steps are executed sequentially i.e. in the
same order in which they appear in the program.
Many a times, we want a set of instructions to be executed in
one situation, and an entirely different set of instructions to be
executed in another situation.
This kind of situation is dealt in C programs using a decision
control instruction
(a) The if statement
(b) The if-else statement
(c) The conditional operators.

The if Statement
General form
if ( this condition is true )
{
execute this statement ;
}
But how do we express the condition itself in C?
we express a condition using C’s ‘relational’ operators.
this expression is true if
x == y x is equal to y
x != y x is not equal to y
x < y x is less than y
x > y x is greater than y
x <= y x is less than or equal to y
x >= y x is greater than or equal to y

/* Demonstration of if statement */
#include<stdio.h>
void main( )
{
int num ;
printf ( "Enter a number less than 10 " ) ;
scanf ( "%d", &num ) ;
if ( num <= 10 )
printf ( "What an obedient servant you are !" ) ;
}

While purchasing certain items, a discount of 10% is offered if
the quantity purchased is more than 1000. If quantity and price
per item are input through the keyboard, write a program to
calculate the total expenses.
void main( )
{
int qty, dis = 0 ;
float rate, tot ;
printf ( "Enter quantity and rate " ) ;
scanf ( "%d %f", &qty, &rate) ;
if ( qty > 1000 )
dis = 10 ;
tot = ( qty * rate ) - ( qty * rate * dis / 100 ) ;
printf ( "Total expenses = Rs. %f", tot ) ;

The current year and the year in which the employee joined the
organization are entered through the keyboard. If the number of
years for which the employee has served the organization is
greater than 3 then a bonus of Rs. 2500/- is given to the
employee. If the years of service are not greater than 3, then
the program should do nothing.

#include<stdio.h>
void main( )
{
int bonus, cy, yoj, yr_of_ser ;
printf ( "Enter current year and year of joining " ) ;
scanf ( "%d %d", &cy, &yoj ) ;
yr_of_ser = cy - yoj ;
if ( yr_of_ser > 3 )
{
bonus = 2500 ;
printf ( "Bonus = Rs. %d", bonus ) ;
}
}

The Real Thing
General form
{ execute this statement ; }
But if ( expression )
{ execute this statement ; }
expression can be any valid expression
if ( 3 + 2 % 5 )
printf ( "This works" ) ;
if ( a = 10 )
printf ( "Even this works" ) ;
if ( -5 )
printf ( "Surprisingly even this works" ) ;
C a non-zero value is considered to be true, whereas a 0 is
considered to be false.

The if-else Statement
Can we execute one group of statements if the expression
evaluates to true and another group of statements if the
expression evaluates to false?
Of course! This is what is the purpose of the else statement
General Form
{
}
else
{
}

The group of statements after the if upto and not including the
else is called an ‘if block’. Similarly, the statements after the
else form the ‘else block’.
Notice that the else is written exactly below the if.
Had there been only one statement to be executed in the if
block and only one statement in the else block we could have
dropped the pair of braces.
As with the if statement, the default scope of else is also the
statement immediately after the else.

Example. In a company an employee is paid as under: If his
basic salary is less than Rs. 1500, then HRA = 10% of basic
salary and DA = 90% of basic salary. If his salary is either
equal to or above Rs. 1500, then HRA = Rs. 500 and DA =
98% of basic salary. If the employee's salary is input through
the keyboard write a program to find his gross salary.

#include<stdio.h>
void main( )
{
float bs, gs, da, hra ;
printf ( "Enter basic salary " ) ;
scanf ( "%f", &bs ) ;
if ( bs < 1500 )
{
hra = bs * 10 / 100 ;
da = bs * 90 / 100 ;
}
else
{
hra = 500 ;
da = bs * 98 / 100 ;
}
gs = bs + hra + da ;
printf ( "gross salary = Rs. %f", gs ) ;

Nested if-elses
if we write an entire if-else construct within either the body of the if
statement or the body of an else statement. This is called ‘nesting’ of ifs.
if ( condition )
{
if ( condition )
do this ;
else
{
do this ;
and this ;
}
}
else
do this ;

#include<stdio.h>.
void main( )
{
int i ;
printf ( "Enter either 1 or 2 " ) ;
scanf ( "%d", &i ) ;
if ( i == 1 )
printf ( "You would go to heaven !" ) ;
else
{
if ( i == 2 )
printf ( "Hell was created with you in mind" ) ;
else
printf ( "How about mother earth !" ) ;
}

Forms of if
The if statement can take any of the following forms:
(a) if ( condition )
do this ;
(b) if ( condition )
{
do this ;
and this ;
}
(c) if ( condition )
do this ;
else
do this ;

Forms of if
(d) if ( condition )
{
do this ;
and this ;
}
else
{
do this ;
and this ;
}

Forms of if
(e) if ( condition )
do this ;
else
{
if ( condition )
do this ;
else
{
do this ;
and this ;
}
}

(f) if ( condition )
{
if ( condition )
do this ;
else
{
do this ;
and this ;
}
}
else
do this ;

Use of Logical Operators
C allows usage of three logical operators, namely, &&, || and !.
These are to be read as ‘AND’ ‘OR’ and ‘NOT’ respectively.
The first two operators, && and ||, allow two or more
conditions to be combined in an if statement.

Fcp chapter 2 upto_if_else (2)

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