CONTROLSTRUCTURES.ppt

CONTROL STRUCTURES
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• Branching: if-else
• Looping: while-do while-for
• Nested control structures
• Switch
• Break
• Continue
• Comma
• goto

Three kinds of execution flow
◦ Sequence:
 The execution of the program is sequential.
◦ Selection / Branching
 A control structure which chooses alternative to execute/program chooses to
follow one branch or another
 Example: if, if/else, switch, Conditional operator
◦ Repetition / Looping
 A control structure which repeats a group of statements.
 Example: while, do/while, for, nested loops, break ,
continue.
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BRANCHING :IF-ELSE STATEMENT
 Simple if
 Multiple if
 if-else
 if-else if ladder
 Nested if-else
 Switch-Case
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The simple if Statement
 The if statement has the following syntax:
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if ( condition )
statement;
if is a C
reserved word
Condition is an expression that is
either false (represented by 0) or
true (represented by 1/non-zero).
If the condition is true, the statement is executed.
If the condition is false, the statement is not executed ,control
comes out

Branching/ Decision
Flow chart for if statement
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The if-else Statement
 An if statement can be followed by an optional else statement,
which executes when the boolean expression is false.
 Syntax:
if(boolean_expression) // eg: A>0
{
True statements; // A is positive
else
{
False statements; //B is negative
}
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The if-else Statement- flow
void main()
{
int age;
scanf(“age=%d “,&age);
if (age>= 18)
{
printf(“Eligible");
}
else
printf(“Not eligible”);
}
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OUTPUT 1
Age=30
Eligible
OUTPUT 2
Age=12
Not Eligible

The if-else Statement-Program to find the given number is odd or even
#include <stdio.h>
void main( )
{
int num;
printf("Enter a number you want to check.n");
scanf("%d",&num);
if((num%2)==0) //checking whether remainder is 0 or not.
printf("%d is even.",num);
else
printf("%d is odd.",num);
}
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OUTPUT
Enter a number you want to check.
25
25 is odd.
Enter a number you want to check.
2
2 is even.

Sample programs
 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.
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/* Calculation of gross salary */
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 ) ;
}
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(if...elseif....else / else-if ladder Statement)
 The if...else if statement is used when program requires more than one test expression
if (test expression1)
{
statement/s to be executed if test expression1 is true;
}
else if(test expression2)
{
statement/s to be executed if test expression1 is false and 2 is true;
}
.
.
.
.
else
{
statements to be executed if all test expressions are false;
}
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To print given number is positive or negative or
zero-using elseif ladder
#include <stdio.h>
int main()
{
int num;
printf("Enter a number n");
scanf("%d",&num);
if (num > 0)
{
printf(“number %d is
positiven“,num);
}
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else if (num < 0)
{
printf(“number %d is
negativen“,num);
}
else if (num = = 0)
{
printf(“number is zero “);
}
printf(“Thank you”);
}

Nested if else Statement
 It is always legal in C programming to nest if-else statements, which means you can
use one if or else if statement inside another if or else
Syntax:
if(cond 1)
{
/* Executes when the boolean expression 1 is true */
if(cond 2)
{
}
else
{ /* Executes when the boolean expression 2 is false */
}
}
else
{ if(cond3)
{
}
else
{ /* Executes when the boolean expression 3 is false */
} 13

Largest of three numbers-Nested if else Statement
#include <stdio.h>
void main ()
{
int a, b,c ;
printf(“enter values a,b and cn”);
scanf(“%d%d%d”,a&a,&b,&c);
if( a >b )
{
if( a>c)
{
printf("a is largestn" );
}
else
{
printf(“c is largestn" );
}
}
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else
{
if( b> c )
{
printf(“b is largestn" );
}
else
{
printf(“c is largestn" );
}
}
}

Nested if else Statement
#include <stdio.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 );
return 0;
}
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OUTPUT
Value of a is 100 and b is 200
Exact value of a is : 100
Exact value of b is : 200

Sample programs
The marks obtained by a student in 5 different subjects
are input through the keyboard. The student gets a
division as per the following rules:
Percentage above or equal to 60 - First division
Percentage between 50 and 59 - Second division
Percentage between 40 and 49 - Third division
Percentage less than 40 - Fail
Write a program to calculate the division obtained by the
student.
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main( )
{
int m1, m2, m3, m4, m5, per ;
printf ( "Enter marks in five subjects " ) ;
scanf ( "%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5 ) ;
per = ( m1 + m2 + m3 + m4 + m5 ) / 5 ;
if ( per >= 60 )
printf ( "First division ") ;
else
{
if ( per >= 50 )
printf ( "Second division" ) ;
else
{
if ( per >= 40 )
printf ( "Third division" ) ;
else
printf ( "Fail" ) ;
}
}
}
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main( )
{
int m1, m2, m3, m4, m5, per ;
printf ( "Enter marks in five subjects " ) ;
scanf ( "%d %d %d %d %d", &m1, &m2, &m3, &m4, &m5 ) ;
per = ( m1 + m2 + m3 + m4 + m5 ) / 5 ;
if ( per >= 60 )
printf ( "First division" ) ;
if ( ( per >= 50 ) && ( per < 60 ) )
if ( ( per >= 40 ) && ( per < 50 ) )
if ( per < 40 )
printf ( "Fail" ) ;
}
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main( )
{
int m1, m2, m3, m4, m5, per ;
per = ( m1+ m2 + m3 + m4+ m5 ) / per ;
if ( per >= 60 )
printf ( "First division" ) ;
else if ( per >= 50 )
else if ( per >= 40 )
else
printf ( "fail" ) ;
}
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A certain grade of steel is graded according to the following conditions:
(i) Hardness must be greater than 50
(ii) Carbon content must be less than 0.7
(iii) Tensile strength must be greater than 5600
The grades are as follows: Grade is 10 if all three conditions are met
Grade is 9 if conditions (i) and (ii) are met
Grade is 8 if conditions (ii) and (iii) are met
Grade is 7 if conditions (i) and (iii) are met
Grade is 6 if only one condition is met
Grade is 5 if none of the conditions are met
Write a program, which will require the user to give values of hardness, carbon
content and tensile strength of the steel under consideration and output the grade
of the steel.
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Calculate the EB bill using if-else-if ladder
Get the no. of units (n)
Units 1 to 100 Amount: Rs. 3.00 per unit
More than 350 Amount: Rs. 7.00 per unit
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To print ASCIIvalues(ifelseif)
 Any character is entered through the keyboard, write a
program to determine whether the character entered is
a capital letter, a small case letter, a digit or a special
symbol. The following table shows the range of ASCII
values for various characters.
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Characters
A – Z
a – z
0 – 9
special symbols
ASCII Values
65 – 90
97 – 122
48 – 57
0 - 47, 58 - 64,
91 - 96, 123 - 127

Switch Statement Syntax
switch(expr/var)
{
case constant-expression :
statement(s);
break; /* optional */
case constant-expression :
statement(s);
break; /* optional */
/* you can have any number of case statements */
default : /* Optional */
}
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main( )
{
int i = 2 ;
switch ( i )
{
case 1 :
printf ( "I am in case 1 n" ) ;
case 2 :
case 3 :
default :
printf ( "I am in default n" ) ;
}
}
The output of this program would be:
I am in case 2
I am in case 3
I am in default

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main( )
{
int i = 22 ;
switch ( i )
{
case 121 :
break ;
case 7 :
break ;
case 22 :
break ;
default :
}
}
I am in case 22

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void main()
{
char c = 'x' ;
switch ( c )
{
case 'v' :
printf ( "I am in case v n" ) ;
break ;
case 'a' :
printf ( "I am in case a n" ) ;
break ;
case 'x' :
printf ( "I am in case x n" ) ;
break ;
default :
}
}
I am in case x

Example 1
scanf(“%d”, &day);
switch ( day )
{
case 0:
printf (“Sundayn”) ;
break ;
case 1:
printf (“Mondayn”) ;
break ;
case 2:
printf (“Tuesdayn”) ;
break ;
case 3:
printf (“Wednesdayn”);
break ;
case 4:
printf (“Thursdayn”) ;
break ;
case 5:
printf (“Fridayn”) ;
break ;
case 6:
printf (“Saturdayn”) ;
break ;
default:
printf (“Error -- invalid
day.n”) ;
break ;
}
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Example 2
#include<stdio.h>
void main()
{
char a;
printf("Enter any Alphabet : ");
scanf("%c",&a);
switch (a)
{
case'A':
case'a':
case'E':
case'e':
case‘I':
case'i':
case'O':
case'o':
case'U':
case'u': printf("It is a Vowel");
break;
default: printf("It is a Consonent");
}
}
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Example 3
#include <stdio.h>
int main ()
{
char grade;
scanf(“%c”, &grade);
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 ); }
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Example 4
#include <stdio.h>
int main ()
{
int a,b,c,choice;
scanf(“%d %d”, &a,&b);
printf(“Menu 1.Add 2.Sub
3.Mul 4.Div 5.Modn”);
scanf(“%d”,&choice);
switch(choice)
{
case 1 :c=a+b;
printf(“Sum is %dn“,c );
break;
case 2:c=a-b;
printf(“Difference is %dn“,c );
break;
case 3:c=a*b;
printf(“Multiply is %dn“,c );
break;
case 4:c=a/b;
printf(“Division is %dn“,c );
break;
case 5:c=a%b;
printf(“Remainder is %dn“,c );
break;
default :
printf("Invalid Choicen" );
} } 32

 Cannot do with switch:
1. A float expression cannot be tested .
2. Cases cannot have variable expressions(eg: case a+3)
3. Multiple cases cannot use same expressions
Eg: case 3: case 1+2:
 Switch is faster than if-else ladder when more conditions
to be tested (because switch matches the value but in if-
else all conditions are evaluated)
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Switch vs if-else ladder

Switch vs if-else ladder
 A nested if-else structure is just as efficient as a switch
statement.
 However, a switch statement may be easier to read.
 Also, it is easier to add new cases to a switch
statement than to a nested if-else structure.
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CONTROLSTRUCTURES.ppt

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