SEQUENCE STATEMENT:
A sequential statement control structure
is a linear structure. It executes statements one after another in a sequence.
There is no mechanism for choosing alternate paths in statement flow. It
executes one statement then automatically moves to next statement and so on.
Example: //
Program to show sequence flow
#include<stdio.h>
#include<conio.h>
void
main()
{
printf("
I am in grade XII.\n");
printf("
I am a student of computer science.");
getch();
}
Flow chart of Sequence:
Decision
making or Control or Selection statement:
The
statement which display one statement when the condition is true, otherwise
display another statement is known as decision-making statement. Since these
statement “control” the flow of execution, they are also known as control statement.
C
language has following types of decision making statements are available as
follows:
a)
Simple if statement
b)
if –else statement
c)
Nested if-else statement
d)
else---if ladder
e)
Switch –case statement
a)
Simple if Statement
The
general form of a simple if
statement is:
if (test
condition)
statement-block;
}
statement-x;
The
‘statement-block’ may be a single statement or a group of statements. If the
test expression is true, the statement block will be executed; otherwise the
statement-block will be skipped and the execution will jump to the statement-x.
Remember, when the condition is true both the statement block and the
statement-x are executed in sequence.
Consider
the following segment of a program that is written for processing of marks
obtained in an entrance examination.
………………….
………………….
if
(category= = sports)
{
Marks=
marks + bonus_marks;
}
printf(“
%f ”,marks);
………………….
………………….
The
program tests the type of category of the student. If the student belongs to
the SPORTS category, then additional bonus_marks are added to his marks before
they are printed. For others, bonus_marks are not added.
b)
if---else statement
The if --- else statement is an extension of the
simple if statement.
If the test expression is true, then the true-block
statements, immediately following the if statement are executed; otherwise, the
false-block statements are executed. In either case, either true-block or false
block will be executed, not both. This is shown in flowchart below. In both the
cases, the control is transferred subsequently to the statement-x.
|
Syntax:
if (test expression)
{
True –block statement(s);
}
else
{
False-block statement(s);
}
Statement-x
|
|
Let us consider an example of counting the
number of boys and girls in a class. We use code 1 for a boy and 2 for a girl.
The program statement to do this may be written as follows.
………………….
………………….
if(code=
= 1)
boy=
boy+1;
if(code=
= 2)
girl=girl+1;
………………….
………………….
The
first test determines whether or not the student is a boy. If yes, the number
of boys is increased by 1 and the program continues to the second test. The
second test again determines whether the student is a girl. This is
unnecessary. Once a student is identified as a boy, there is no need to test
again for a girl, not both. The above program segment can be modified using the
else clause as follows.
………………….
………………….
if(code
= = 1)
boy=boy+1;
else
girl=girl+1;
………………….
c)
Nested if ----- else statement
When
a series of decisions are involved, we may have to use more than one if
----else statement in nested form as shown below:
if (test condition-1)
{
if
(test condition-2)
{
Statement-1;
}
else
{
Statement-2;
}
}
else
{
Statement-3;
}
Statement-x;
If
the condition-1 is false, the statement-3 will be executed; otherwise it
continues to perform the second test. If the condition-2 is true, the statement
-1 will be executed; otherwise the statement-2 will be executed and then the
control is transformed to the statement –x.
A
commercial bank has introduced an incentive policy of giving bonus to all its
deposit holders. The policy is as follows: A bonus of 2% of the balance held on
31st December is given to everyone, irrespective of their balance,
and 5% is given to female account holders if their balance is more than Rs.
5000. This logic can be coded as follows:
…….
if(sex
is female)
{
if(balance
>5000)
bonus=0.05*balance;
else
bonus=0.02*balance;
}
else
{
bonus=0.02*balance;
}
balance=balance+bonus;
……………
The
logic of execution is illustrated in figure below.
d) The else---if
ladder
This
is another way of putting ifs together when multipath decisions are involved. A
multipath decision is a chain of ifs in which the statement associated with
each else is an if.
It
takes the following general form:
if
(condition 1)
statement-1;
else
if (condition 2)
statement-2;
else
if (condition 3)
statement-3;
else
if (condition n)
statement-n;
else
default - statement;
statement
–x;
This
construct is known as the else - - if ladder. The conditions are evaluated from
the top (of the ladder) to downwards. As soon as a true condition is found, the
statement associated with it is executed and the control is transferred to the
statement – x (skipping the rest of ladder). When all the “n” conditions become
false, then the final else containing the default – statement will be executed.
Let
us consider an example of grading the students in an academic instituting.
The
grading is done according to the following rules:
|
Average
Marks
|
Grade
|
|
80
to 100
|
Distinction
|
|
60
to 79
|
First
Division
|
|
50
to 59
|
Second
Division
|
|
40
to 49
|
Third
Division
|
|
0
to 39
|
Fail
|
This
grading can be done using the else if ladder as follows:
if(marks>79)
grade=”Distinction”;
else
if(marks>59)
grade=”First Division”;
else
if(marks>49)
grade=”Second Division”;
else
if(marks>39)
grade=”Third Division”;
else
grade=”Fail”;
printf(“%s\n”,grade);
e) Switch- Case
Statement
The
switch statement tests the value of a given variable (or expression) against a
list of case values and when a match is found, a block of statements associated
with that case is executed.
The
general form of the switch statement is as shown below:
switch(expression)
{
case
value-1:
block-1;break;
case
value-2:
block-2;
break;
…………………….
…………………….
default:
default
– block;
break;
}
statement
– x;
When
the switch is executed, the value of the expression is successfully compared
against the values value-1,value-2,..
If
a case is found whose value matches with the value of the expression, then the
block of statements that follow the case are executed.
The
break statement at the end of each
block signals the end of a particular case and causes an exit from the switch
statement, transferring the control to the statement-x following with switch.
The
default is an optional case. When
present, it will be executed if the value of the expression does not match with
any of the case values. If not present, no action takes place if all matches
fail and the control goes to the statement-x.
Let
us consider an example, which displays the name of 7 days according to input
numbers.
This can be shown as follows:
Program to display 1 for Sunday, 2 for Monday and so
on.
#include<stdio.h>
void main ( )
{
int choice;
printf("Enter
the number of the day=");
scanf("%d",&choice);
switch(choice)
{
case
1:
printf("Sunday");
break;
case
2:
printf("Monday");
break;
case
3:
printf("Tuesday");
break;
case
4:
printf("Wednesday");
break;
case
5:
printf("Thursday");
break;
case
6:
printf("Friday");
break;
case
7:
printf("Saturday");
break;
default:
printf("Wrong
Choice");
}
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