Decision makingandbranching in c

DECISION MAKING AND
BRANCHING
3-May-20 Decision making branching 1

DECISION MAKING…
• Decision making is about deciding the order of
execution of statements based on certain
conditions or repeat a group of statements
until certain specified conditions are met.
• Since they control the flow of statements also
called as Control Statements
• Two types:
- Conditional control statements
-unconditional control statements

Decision Making -Examples
• C language handles decision-making by supporting
the following statements:
Conditional Statements are:
if statement
switch statement
conditional operator statement (? : operator)
Unconditional Statements are:
goto statement

DECISION MAKING WITH ‘IF’
- If is powerful decision making statement hence
called as two way decision making statement
Syntax:
If(test expression);
False

DECISION MAKING WITH ‘IF’
- The if statement may be implemented in different
forms depending on the complexity of conditions to
be tested. The different forms are
• Simple if statement
• if....else statement
• Nested if....else statement
• Using else if statement

SIMPLE ‘IF’
- The statements inside the body of “if” execute if
the given condition returns true.
- If the condition returns false then the statements
inside “if” are skipped.
- If condition is true both the block of statements
and next statement is executed
- The statement-block may be single or block of
statements

SIMPLE ‘IF’
SYNTAX FLOWCHART
if (test condition)
{
block of
statements;
... ... ...
}
statement-x;

SIMPLE ‘IF’
Program:
#include <stdio.h>
void main( )
{
int x, y;
x = 15;
y = 13;
if (x > y )
{
printf("x is greater than y"); }}
O/P:
x is greater than y

‘IF… ELSE’ STATEMENT
- It consists of two blocks of statements each enclosed
inside if block and else block
- If the condition is true, statements True block statement
will be executed
- otherwise statements inside else block are executed.
- In either case, only one block is executed ,not both .

‘IF… ELSE’ STATEMENT
Syntax FLOWCHART
if (test condition)
{
true block statements;
... ... ...
}
else
{
false block statements;
... ... ...
}
statement x;

Example: If… else Statement
Program
#include<stdio.h>
void main()
{
int n;
printf("Enter a number:");
scanf("%d",&n);
if(n%2 == 0)
printf("%d is even",n);
else
printf("%d is odd",n);
getch();
}
Output:
Enter a number: 3
3 is odd

NESTING OF ‘IF … ELSE’ STATEMENT
- executes two different codes depending upon
whether the test expression is true or false.
- Sometimes, a choice has to be made from more
than 2 possibilities.
- allows to check for multiple test expressions and
execute different codes for more than two
conditions.

Syntax: Nested if else
if(test condition1)
{
If(test condition2)
{
statement block1;
}
else
{
statement block2;
}
}
else
{
statement block3;
}
statement –x;

Flowchart: Nested if… else

Example: Nested if…else
Program:
void main()
{
float a,b,c;
printf(“ Enter Three values”);
scanf(“%f%f%f”, &a,&b,&c);
printf(“largest value is”);
if(a>b)
{
if(a>c)
printf(“%fn”,a)
else
printf(“%fn”,c)
}
else
{
if(c>b)
printf(“%fn”,c)
else
printf(“%fn”,b)
}
getch();
}
Output:
Enter Three values
22.22 87.43 67.45
Largest value is 87.43

else…if Ladder
- to test set of conditions in sequence called as
multipath decisions
- statements are evaluated from top to bottom
- As soon as the true statement is found, the
statement associated with it is executed
- the control is transferred to the statement-x
(Skipping the rest of the conditions)
- when all the ‘n’ conditions become false, the
final else, containing the default-statement will
be executed3-May-20 Decision making branching 16

Syntax: else…if Ladder
if(condition-1)
{
statements;
}
else if
(condition-2)
{
statements;
}
else if
(condition-3)
{
statements;
}
:
:
else
{
statements;
}3-May-20 Decision making branching 17

Example: else…if Ladder
#include<stdio.h>
void main()
{
int mark;
printf(“Enter Mark:”);
scanf(“%d”, &mark);
if(mark= = 100)
{
printf(“Centum Result”);
}
else if
if((mark >=75 )&&(mark<=99)
{
printf(“Merit Result”);
}
else if
if((mark>=60 )&&(mark<=75)
{
printf(“First Class Result”);
}
else if
if(mark>=40 )&&(mark<=59)
{
printf(“Pass Result”);
}
else
printf(“Fail Result”);
}
getch();
}

Output:
Enter Marks: 79
First Class Result

SWITCH CASE
- Switch is also called as multiway decision statement
- allows to choose only one choice among the many
given choices
- allows a variable to be tested for equality against a list
of values
- The expression in switch evaluates to return an
integral value, which is then compared to the values
present in different cases.
- It executes that block of code which matches the case
value.
- If there is no match, then default block is executed (if
present)3-May-20 Decision making branching 21

SYNTAX: SWITCH CASEswitch(expression)
{
case value-1 :
block-1;
break; /* optional */
case value-2 :
block-2;
case value-n :
block-n;
:
default :
default-block;
break; /* Optional */
}

SWITCH CASE
- The expression is an integer expression or
characters
- value-1,value-2 are constants or constant
expression also called as case labels
- block1,block2 are statement lists may contain zero
or more statements
- Case labels end with colon(:)
- Break statement at the end of each block signals
the end of particular case and cause an exit from
switch
- Default is an optional case3-May-20 Decision making branching 23

Rules for SWITCH Statement
- The switch expression must be an integral type
- Case labels must be constant or constant
expression.
- Case labels must be unique end with colon(:)
- Break statement transfers the control out of the
switch statement
- Break and default is an optional.
- There can be atmost one default label
- Default may be placed anywhere but usually
placed at the end

The ?: operator
- The conditional operator (? :) is a ternary
operator(it takes three operands), makes two-way
decisions.
- Conditional operator is closely related
with if..else statement.
- If the condition is true then expression1 is
executed else expression2 is executed.3-May-20 Decision making branching 27

The ?: operator
Program:
#include <stdio.h>
int main()
{
int mark;
printf("Enter mark: ");
scanf("%d", &mark);
puts(mark >= 40 ? "Passed" :
"Failed");
return 0;
}
Output
Enter mark:
39 Failed
Explanation
The program checks the
condition mark >=40, if it is
true "Passed" is printed
else "Failed".

GOTO STATEMENT
- Got statement is used to branch unconditionally
from one point to another in the program
- the control jumps directly to the label mentioned
in the ‘goto’ statement
- A label is an identifier required for ‘goto’
statement to a place where the branch is to be
made
- Label can be anywhere in the program either
before or after the goto label
- It breaks the normal sequence of the program

GOTO STATEMENT
Defining a label: label_name:
- label_name should be a valid identifier name.
- : (colon) should be used after the label_name.
-If the label: is before the statement goto label;
a loop will be formed and some statements will be
executed repeatedly called as Backward jump
-If the label: is placed after the goto label;
some statements will be skipped and the jump is
known as forward jump

SYNTAX: GOTO STATEMENT
Forward jump
goto label;
... .. ...
... .. ...
... .. ...
label:
statement;
Backward Jump
label:
statement;
... .. ...
... .. ...
... .. ...
goto label;
;

Flowchart of gotostatemet

EXAMPLE: BackwardGOTO STATEMENT
include <stdio.h>
int main()
{
int number;
number=1;
repeat:
printf("%dn",number);
number++;
if(number<=10)
goto repeat;
return 0;
}
Output:
1
2
3
4
5
6
7
8
9
10

EXAMPLE: GOTO STATEMENT
#include <stdio.h>
void main()
{
int number;
printf("Enter an integer number: ");
scanf("%d",&number);
if(number<=0)
goto end;
printf("Number is : %d", number);
end: printf("Bye Bye !!!");
}
Output:
First run:
Enter an integer
number: 123
Number is : 123
Bye Bye !!!
Second run:
Enter an integer
number: 0
Bye Bye !!!

MAHENDIRAN N
ASSISTANT PROFESSOR
Department of Computer Science
Sri Ramakrishna College of Arts and Science
Coimbatore - 641 006
Tamil Nadu, India
35

Decision makingandbranching in c

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