Bsc cs pic u-3 handling input output and control statements

Handling
Input/output
&
Control StatementsCourse: BSC CS
Subject: Programming In C Language

CONTROL STATEMENTS
 C language supports the following statements known
as control or decision making statements.
1. if statement
2. switch statement
3. conditional operator statement
4. Go to statement

IF STATEMENT
 The if statement is used to control the flow of
execution of statements and is of the form
 If(test expression)
 Eg:
if(bank balance is zero)
Borrow money

Cont..
 The if statement may be implemented in different
forms depending on the complexity of conditions
to be tested.
1. Simple if statement
2. if…..else statement
3. Nested if…..else statement
4. elseif ladder

The general form of a simple
if statement is The
‘statement-block’ may be a
single statement or a group
of statement
If(test exprn)
{
statement-block;
}
statement-x;
Cont..

THE IF…ELSE STATEMENT
 The if….else statement is an extension of simple if
statement. The general form is
If(test expression)
{
True-block statement(s)
}
else
{
False-block statement(s)
}
statement-x

Cont..
 If the test expression is true, then the true block statements
are executed; otherwise the false block statement will be
executed.

Cont..
 Eg:
………
………
if(code ==1)
boy = boy + 1;
if(code == 2)
girl =girl + 1;
………
………

NESTING OF IF…..ELSE STATEMENTS
 When a series of decisions are involved, we may have
to use more than one if….else statements, in nested
form as follows

Cont..
Here, if the condition 1 is false then it
skipped to statement 3.
But if the condition 1 is true, then it
tests condition 2.

If condition 2 is true then it executes
statement 1 and if false then it executes
statement 2.
 Then the control is transferred to the
statement x.
This can also be shown by the following
flowchart,

Program
/*Selecting the largest of three values*/
main()
{
float A, B, C;
printf(“Enter three values n”);
scanf(“|%f %f %f”,&A, &B, &C);
printf(“nLargest value is:”);
if(A > B)
{ if(A > C)
printf(“%f n”,A);
else
printf(“%f n”,C);
}
else
{
if(C > B)
printf(“%f n”,C);
else
printf(“%f n”,B);
}
}
 OUTPUT
 Enter three values:
 5 8 24
 Largest value is 24

The else if ladder
When a multipath decision is involved then we use else if ladder.
 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,

Cont..
 This construct is known as the else if ladder. The conditions are
evaluated from the top, downwards. This can be shown by the
following flowchart

THE SWITCH STATEMENT
 Switch statement is used for complex programs when
the number of alternatives increases.
 The switch statement tests the value of the given
variable against the list of case values and when a
match is found, a block of statements associated with
that case is executed.

SWITCH STATEMENT
 The general form of switch statement is
switch(expression)
{
case value-1:
block-1
break;
case value-2:
block-2
break;
…….
…….
default:
default-block
break;
}
statement-x;

Example:
index = marks / 10;
switch(index)
{
case 10:
case 9:
case 8:
grade = “Honours”;
break;
case 7:
case 6:
grade = “first division”;
break;
case 5:
grade = “second
division”;
break;
case 4:
grade = “third
division”;
break;
default:
grade = “first
division”; break
}
printf(“%s n”,grade);
………….

THE ?: OPERATOR
 The C language has an unusual operator, useful for making two-
way decisions.
 This operator is a combination of ? and : and takes three
operands.
 It is of the form exp1?exp2:exp 3
 Here exp1 is evaluated first. If it is true then the expression exp2 is
evaluated and becomes the value of the expression.
 If exp1 is false then exp3 is evaluated and its value becomes the
value of the expression.
Eg:
if(x < 0)
flag = 0;
else
flag = 1;
can be written as
flag = (x < 0)? 0 : 1;

UNCONDITIONAL STATEMENTS - THE GOTO STATEMENT
C supports the goto statement to
branchunconditionally from one point of the
program to another.
The goto requires a label in order to identify
the place where the branch is to be made.
A label is any valid variable name and
must be followed by a colon.

DECISION MAKING AND LOOPING
 In looping, a sequence of statements are executed until some
conditions for termination of the loop are satisfied.
 In looping, a sequence of statements are executed until some
conditions for termination of the loop are satisfied.
 A program loop therefore consists of two segments, one known
as the body of the loop and the other known as the control
statements.

Cont..
Depending on the position of the control statements in
the loop, a control structure may be classified either as an
entry-controlled loop or as the exit-controlled loop.

Loops In C
 The C language provides for three loop constructs for
performing loop operations.
 They are:
The while statement
The do statement
The for statement

THE WHILE STATEMENT
 The basic format of the while statement is
while(test condition)
{
body of the loop
}
 The while is an entry–controlled loop statement.
 The test-condition is evaluated and if the condition is true, then the
body of the loop is executed.
 After execution of the body, the test-condition is once again evaluated and
if it is true, the body is executed once again.
 This process of repeated execution of the body continues until the test-
condition finally becomes false and the control is transferred out of the loop.

Example of WHILE Loop
-----------
-----------
Body of the loop
test
condn?
while(test condition)
{
body of the loop
}
sum = 0;
n = 1;
while(n <= 10)
{
sum = sum + n* n;
n = n + 1;
}
printf(“sum = %d n”,sum);
-----------
-----------

THE DO STATEMENT
 In while loop the body of the loop may not be executed at
all if the condition is not satisfied at the very first attempt.
 Such situations can be handled with the help of the do
statement.
do
{
body of the loop
}
while(test condition);

Cont..
 Since the test-condition is evaluated at the bottom of the loop,
the do…..while construct provides an exit-controlled loop and
therefore the body of the loop is always executed at least once.
Eg:
-----------
do
{
printf(“Input a numbern”);
number = getnum();
}
while(number > 0);
-----------

THE FOR STATEMENT
 The for loop is another entry-controlled loop that
provides a more concise loop control structure
 The general form of the for loop is
for(initialization ; test-condition ; increment
{
body of the loop
}

Cont..
 The execution of the for statement is as follows:
 Initialization of the control variables is done first.
 The value of the control variable is tested using the test-condition.
 If the condition is true, the body of the loop is executed; otherwise
the loop is terminated and the execution continues with the
statement that immediately follows the loop.
 When the body of the loop is executed, the control is transferred
back to the for statement after evaluating the last statement in
the loop.
 Now, the control variable is either incremented or decremented as
per the condition.

For Statement
 Eg 1)
for(x = 0; x <= 9; x = x + 1)
{
printf)”%d”,x);
}
printf(“n”);
 The multiple arguments in the increment section are possible
and separated by commas.

Cont..
 Eg 2)
sum = 0;
for(i = 1; i < 20 && sum <100; ++i)
{
sum =sum + i;
printf(“%d %d n”,sum);
}
for(initialization ; test-condition ; increment
{
body of the loop
}

Nesting of For Loops
 C allows one for statement within another for
statement.

Cont..
 Eg:
 ----------
 ----------
 for(row = 1; row <= ROWMAX; ++row)
 {
 for(column = 1; column < = COLMAX; ++column)
 {
 y = row * column;
 printf(“%4d”, y);
 }
 printf(“n”);
 }
 ----------
 ----------

JUMPS IN LOOPS
 C permits a jump from one statement to another within a
loop as well as the jump outof a loop.
Jumping out of a Loop
 An early exit from a loop can be accomplished by using the
break statement or the goto statement.
 When the break statement is encountered inside a loop, the
loop is immediately exited and the program continues with
the statement immediately following the loop.
 When the loops are nested, the break would only exit from
the loop containing it. That is, the break will exit only a
single loop.

Skipping a part of a Loop
 Like the break statement, C supports another similar
statement called the continue statement.
 However, unlike the break which causes the loop to be
terminated, the continue, as the name implies, causes the
loop to be continued with the next iteration after skipping
any statements in between.
 The continue statement tells the compiler, “SKIP THE
FOLLOWING STATEMENTS AND CONTINUE WITH THE NEXT
ITERATION”.
 The format of the continue statement is simply
continue;

Bypassing and continuing I Loops

References
1. http://www.computer-books.us/c_0008.php
2. http://www.computer-books.us/c_0009
3. http://www.computer-books.us/c_2.php
4. www.tutorialspoint.com/cprogramming/cprogramming_pdf.
5. Programming in C by yashwant kanitkar
6. ANSI C by E.balagurusamy- TMG publication
7. Computer programming and Utilization by sanjay shah Mahajan Publication
8. www.cprogramming.com/books.html

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Bsc cs pic u-3 handling input output and control statements