Selection Statements in C Programming

LOGICAL EXPRESSIONS
 IF STATEMENT
SWITCH STATEMENT
Selection Statements

Flow of Control
 Unless specified , the order of statement execution
through a C program is linear: one statement after
the other, in sequence.
 Some programming statements modify that
order, allowing us to:
 decide whether or not to execute a particular statement, or
perform a statement over and over, repetitively

3
Flow of Control
 These decisions are based on a boolean Or logical
expression (also called a condition) that evaluates to
true or false
 The order of statement execution is called the flow of
control

Flow of Control
Sequential Flow

Flow of Control
Selection Statements

Logical Expression
 Logical expression is an expression which uses one
or more logical operators, e.g.,
 (temperature > 90.0 && humidity > 0.90)
 !(n <= 0 || n >= 100).
 The output of the logical expression is the boolean
value either true or false.

If Statements
 If statements consists of boolean expression followed
by one or more statements.
 If the boolean expression evaluates to true, the
statements inside the block get executed otherwise
the first statement outside the block get executed.
 The false value is o and all the other values are
evaluated as true in C.

If Statement
 The syntax of an If statement in C Program is given
below

If…else Statement
 If statements can be followed by the optional else
statements, which get executed when the boolean
expression is false.

If…elseif…else Statement
 If statement can be followed by optional elseif..else
statement, which is very useful to test various
conditions using single if…elseif statement.
 Following things should be kept in mind
 An if can have zero or one else's and it must come after any
else if's.
 An if can have zero to many else if's and they must come
before the else.
 Once an else if succeeds, none of the remaining else if's or
else's will be tested.

If…elseif…else Statement(Example)
#include <stdio.h>
#include<conio.h>
int main ()
{
int a = 100;
if( a == 10 )
{
printf("Value of a is 10n" );
}
else if( a == 20 )
{
}
else if( a == 30 )
{
}
else
{
printf("None of the values is
matchingn" );
}
printf("Exact value of a is:
%dn", a );
getch();
return 0;
}

Nested if Statements
 It is always legal in C programming to nest if-else
statements, which means we can use one if or else if
statement inside another if or else if statement(s).

Nested if Statements
#include <stdio.h>
#include <conio.h>
int main ()
{
int a = 100;
int b = 200;
if( a == 100 )
{
if( b == 200 )
{
printf("Value of a is 100
and b is 200n" );
}
}
printf("Exact value of a is :
%dn", a );
printf("Exact value of b is :
%dn", b );
getch();
return 0;
}

Switch Statement
 A switch statement allows a variable to be tested for
equality against a list of values.
 Each value is called a case, and the variable being
switched on is checked for each switch case.
 The following rules apply to a switch statement:
 The expression used in a switch statement must have an integral or
enumerated type, or be of a class type in which the class has a single
conversion function to an integral or enumerated type.
 You can have any number of case statements within a switch. Each
case is followed by the value to be compared to and a colon.
 The constant-expression for a case must be the same data type as the
variable in the switch, and it must be a constant or a literal.

Switch Statement
 When the variable being switched on is equal to a case, the
statements following that case will execute until a break
statement is reached.
 When a break statement is reached, the switch terminates, and
the flow of control jumps to the next line following the switch
statement.
 Not every case needs to contain a break. If no break
appears, the flow of control will fall through to subsequent
cases until a break is reached.
 A switch statement can have an optional default case, which
must appear at the end of the switch. The default case can be
used for performing a task when none of the cases is true. No
break is needed in the default case.

Switch Statement
#include <stdio.h>
#include <conio.h>
int main ()
{
char grade = 'B';
switch(grade)
{
case 'A' :
printf("Excellent!n" );
break;
case 'B' :
case 'C' :
printf("Well donen" );
break;
case 'D' :
printf("You passedn" );
break;
case 'F' :
printf("Better try againn" );
break;
default :
printf("Invalid graden" );
}
printf("Your grade is
%cn", grade );
getch();
return 0;
}

Nested Switch Statements
 It is possible to have a switch as part of the statement
sequence of an outer switch.
 Even if the case constants of the inner and outer
switch contain common values, no conflicts will
arise.

Nested Switch Statements
#include <stdio.h>
#include <conio.h>
int main ()
{
int a = 100;
int b = 200;
switch(a)
{
case 100:
printf("This is part of outer
switchn", a );
switch(b)
{
case 200:
printf("This is part of inner
switchn", a );
}
}
printf("Exact value of a is : %dn", a
);
printf("Exact value of b is : %dn", b
);
getch();
return 0;
}

Selection Statements in C Programming

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Selection Statements in C Programming