C programming Decision statments

1. Unit-IV
Decision Statements

2. Introduction
 A program is execution of one or more instructions
sequentially in the order in which they come in to sight.
 This process is similar to reading the text that appears in
notebook.
 Quite often it is desirable in a program to alter the sequence
of the statements depending upon certain circumstances.
 Decision making statements in a programming language help
the programmer to transfer the control from one part to other
parts of the program.

3. Introduction (cont..)
 Decision making statements helps the programmer in
determining the flow of control.
 This involves a decision making conditions to see whether the
particular condition is satisfied or not.

4. Decision making statements in C
 if statement
 if –else statement
 if-else-if ladder statement
 nested if-else statement
 switch-case statement
 goto statement

5. if statement
 C uses the keyword if to execute a set of command lines or one command line
when logical condition is true.
void main()
{
if(expression)
{
statement1;
statement2;
}
statement3;
}

6. if statement (continue..)
 If statement contains an expression which is evaluated. If the expression is
true it returns 1 otherwise 0.
 In case the condition is true the compiler execute the lines within if block.
Else compiler skips the lines within if block.
 The conditional statement should not be terminated with semi-colon.
 The multiple statements which are to be executed if condition is true are
enclosed within curly bracket.
 The curly bracket indicates the scope of if statement.

7. if statement (continue…)
void main()
{
if(expression)
{
statement1;
statement2;
}
statement3;
}
void main()
{
if(expression)
statement1;
statement2;
}

8. Write a program to check whether entered number is less than 10. if
yes print the same.
void main()
{
int n;
clrscr();
printf(“enter a number”);
scanf(“%d”, &n);
if(n<10)
printf(“entered number is less than 10);
getch();
}

9. Start
Input
value
of n
If
n<10
Print
message
Stop
True
False

10. Write a program to check whether entered number is less 10 and
greater than 0. if yes print the same.
void main()
{
int n;
clrscr();
printf(“enter a number”);
scanf(“%d”, &n);
if(n<10 && n>0)
printf(“entered number is less than 10 and greater than 0);
getch();
}

11. Output?
main( )
{
int a = 300, b, c ;
if ( a >= 400 )
b = 300 ;
c = 200 ;
printf ( "n%d %d", b, c ) ;
}
main( )
{
int a = 300, b, c ;
if ( a >= 400 )
b = 300 ;
c = 200 ;
printf ( "n%d %d", b, c ) ;
}

12. if-else statement
 if block statement execute only when the condition in if is true.
 When condition is flase, program control executes the next statement
which appear after if statement.
 The if-else statement takes care of the true and false condition.
 It has two blocks. One block is for if and it is executed when the condition
is true.
 The other block is of else and it is executed when the condition is false.
 The else statement can not be used without if.
 No multiple else statements are allowed with one if

13. Is condition
true?
if block execution
else block execution
Next statement
Stop
NO
Yes
From previous statement
If-else
Statement

14. if-else statement (continue..)
void main()
{
if(expression)
{
statement1;
statement2;
}
else
{
statement3;
statement4;
}
}

15. if-else statement
void main()
{
if(expression)
{
statement1;
statement2;
}
else
{
statement3;
statement4;
}
}
void main()
{
if(expression)
statement1;
else
statement2;
}

16. Write a program to add three numbers and after addition check if sum is between of 100
and 200 or not.
void main()
{
int a,b,c,d;
clrscr();
printf(“enter three numbers a,b,c”);
scanf(“%d,%d,%d”,&a, &b, &c);
d=a+b+c;
if(d>100 && d<200)
printf(“n sum is %d which is in between 100 and 200”);
else
printf(“n sum is %d which is out of range”);
getch();
}

17. Output?
main( )
{
int x = 3, y = 5 ;
if ( x == 3 )
printf ( "%d", x ) ;
else
printf ( "%d", y ) ;
}

18. Output?
main( )
{
int i = 65 ;
char j = ‘A’ ;
if ( i == j )
printf ( “C is WOW” ) ;
else
printf( "C is a headache" ) ;
}

19. Find out error
void main( )
{
float a = 12.25, b = 12.52 ;
if ( a = b )
printf ( "na and b are equal" ) ;
}

20. Find out error
main( )
{
int x = 10 ;
if x >= 2
printf ( "n%d", x ) ;
}

21. Find out error
Void main( )
{
int x = 10, y = 15 ;
if ( x % 2 = y % 3 )
printf ( "Equal" ) ;
}

22. Nested if-else statement
if(condition)
{
if(condition)
{
statement1;
statement2;
}
else
{
statement3;
statement4;
}
}

23. else
{
if(condition)
{
statement5;
statement6;
}
else
{
statement7;
statement8;
}
}

24. Is 1st
condition
true?
Is 2nd
condition
true?
Is 3rd
condition
true?
statement4 statement3 Statement2 statement1
Next statement
True
True
True
False
False
False
From previous statement

25. Example
Void main()
{
Int i, age;
Printf (“enter 1 for male and 2 for female”);
Scanf(“%d”, &i);
printf(“Enter your age”);
scanf(“%d”, &age);
If(i==1)
{
if(age>20)
printf(“Eligible for marriage”);
else
printf(“Not eligible for marriage”);

26. If-else-if Ladder statement
 If the first logical condition is true the compiler executes block followed by
first if condition, otherwise it skips that block and checks for next logical
condition followed by else-if and if it is true the block statement followed
by that else-if will be executed.

27. Is 1st
condition
true?
Is 2nd
condition
true?
Is 3rd
condition
true?
Is 4th
condition
true?
STATEMENT 5
STATEMENT 3
STATEMENT 2
STATEMENT 1 STATEMENT 4
FALSE
FALSE
FALSE
FALSE
TRUE
TRUE
TRUE
TRUE
TO NEXT STATEMENT

28. if (condition)
{
Statement 1;
Statement 2;
}
else if(condition)
{
Statement 3;
Statement 4;
}
else
{
Statement 5;
Statement 6;
}

29. goto statement- Unconditional
branching
 This statement does not require any condition for jump.
 This statement passes control anywhere in program.
 Control is passed to another part of program without testing any
condition.
 goto statement can be defined as follows:
goto label;
where label name must start with character.
 The label is the position where the control is to be transferred.

30. goto statement (continue..)
void main()
{
int x;
clrscr();
printf(“enter a number”);
scanf(“%d”,&x);
if(x%2==0)
goto even;
else
goto odd;

31. even: printf(“%d is even”,x);
getch();
return;
odd: printf(“%d is odd”,x);
getch();
}

32. break statement

33. continue statement

34. Switch-case-default
 The control statement that allows us to make a decision from the number
of choices is called a switch,
 or more correctly a switch-case-default, since these three keywords go
together to make up the control statement.

35. switch ( integer expression )
{
case constant 1 :
do this ;
case constant 2 :
do this ;
case constant 3 :
do this ;
default :
do this ;
}

36.  The integer expression following the keyword switch is any C expression
that will yield an integer value.
 It could be an integer constant like 1, 2 or 3, or an expression that
evaluates to an integer.
 The keyword case is followed by an integer or a character constant.
 Each constant in each case must be different from all the others.

37. main( )
{
int i = 2 ;
switch ( i )
{
case 1 :
printf ( "I am in case 1 n" ) ;
case 2 :
printf ( "I am in case 2 n" ) ;
case 3 :
printf ( "I am in case 3 n" ) ;
default :
printf ( "I am in default n" ) ;
}
}

38.  If you want that only case 2 should get executed, it is upto you to get out
of the switch then and there by using a break statement.

39. main( )
{
int i = 2 ;
switch ( i )
{
case 1 :
printf ( "I am in case 1 n" ) ;
break ;
case 2 :
printf ( "I am in case 2 n" ) ;
break ;
case 3 :
printf ( "I am in case 3 n" ) ;
break ;
default :
printf ( "I am in default n" ) ;
}
}

40. SWITCH-CASE
FLOW CHART