Basics of Control Statement in C Languages

1. Subject: Programming In C Language
C. P. Divate

2. CONTROL STATEMENTS
C language supports the following statements known as
control or decision making statements.
1. if statement
2. if…..else statement
3. Nesting of if…..else statement
4. if ……else ladder
5. switchstatement
6. conditional operatorstatement
7. Go tostatement

3. IF( ) STATEMENT
 if statement is the most simple decision making statement.
 It is used to decide whether a certain statement or block of
statements will be executed or not.
 i.e if a certain condition is true then a block of statement is
executed otherwise not.
 Syntax:
if(condition)
{
// Statements to execute if
// condition is true
}
 Example:
if(bank balance is zero)
Borrow money

4. IF( ) STATEMENT
 Here, condition after evaluation
will result either true or false.
 if statement condition results in
boolean values.
 if the value is true then it will
execute the block of statements
below it otherwise not.
 If we do not provide the curly
braces ‘{‘ and ‘}’ after
if(condition) then by default if
statement will consider the first
immediately below statement to
be inside its block.

5. IF( ) STATEMENT Example
// C program to illustrate If ()
#include <stdio.h>
int main()
{
int i = 10;
if (i > 15)
{
printf("10 is less than 15");
}
printf("I am Not in if");
}
Output:
I am Not in if
#include <stdio.h>
int main()
{
int x = 20;
int y = 22;
if (x<y)
{
printf("Variable x is less than y");
}
}
Output1:
Variable x is less than y

6. IF( ) STATEMENT Example
Output1:
Enter a number:4
4 is positive number
// C program to check that no is positive
#include<stdio.h>
int main()
{
int number=0;
printf("Enter a number:");
scanf("%d",&number);
if(number >= 0)
{
printf("%d is positive number",number);
}
}
Output1:
Enter a number: -10

7. IF( ) STATEMENT Example
// C program to check that no is even
#include<stdio.h>
int main()
{
int number=0;
printf("Enter a number:");
scanf("%d",&number);
if(number%2==0)
{
printf("%d is even number",number);
}
}
Output1:
Enter a number:4
4 is even number
Output2:
Enter a number:5

8. IF( ) STATEMENT Example
// C program to check that no is divisible by 7
#include<stdio.h>
int main()
{
int number=0;
printf("Enter a number:");
scanf("%d",&number);
if(number % 7==0)
{
printf("%d is divisible by 7",number);
}
}
Output1:
Enter a number:49
49 is divisible by 7
Output2:
Enter a number:55

9. IF( ) STATEMENT Example
// C to calculate fine in library
#include<stdio.h>
int main()
{
int days;
float fine=0;
printf("Enter no of days:");
scanf("%d",&days);
if(days >=8)
{
fine=(days-8) * 2;
}
printf(“Fine = %f for Total days=%d”, fine, (days-8));
}
Output1:
Enter no of days:10
Fine = 4 for Total days=2
Output1:
Enter no of days:7
Fine = 0 for Total days= -1

10. Multiple IF( ) STATEMENT Example
// C Example of multiple if statements
#include <stdio.h>
int main()
{
int x, y;
printf("enter the value of x:");
scanf("%d", &x);
printf("enter the value of y:");
scanf("%d", &y);
if (x>y)
{
printf("x is greater than yn");
}
if (x<y)
{
printf("x is less than yn");
}
Output1:
enter the value of x:30
enter the value of y:20
x is greater than y
End of Program
Output2:
enter the value of x:20
enter the value of y:20
x is equal to y
End of Program
if (x==y)
{
printf("x is equal to yn");
}
printf("End of Program");
return 0;
}

11. IF( ) STATEMENT Home work Example
 Write a C program to check income is greater than 30000
 Write a C program to calculate income_tax if income is greater than 30000
(formula income_tax=30 % of income)
 Calculate result of student based on following conditions.
if percentage < 35 then fail
if percentage >= 35 then pass

12. IF( ) … else ….STATEMENT
 if statement is the decision making statement.
 An if statement can be followed by an optional else statement, which
executes when the Boolean expression is false.
 i.e if a certain condition is true then a block of statement is executed
otherwise else block statement is executed.
 Syntax:
if (condition) {
// block of code if condition is true
}
else {
// block of code if condition is false
}

13.  Here, condition after evaluation
will result either true or false.
 if statement condition results in
boolean values.
 if the value is true then it will
execute the true block of if
statements below it otherwise it
will execute the false block(else
block of if statements .
IF( ) … else ….STATEMENT

14. IF( ) … else ….STATEMENT Example

15. IF( ) … else ….STATEMENT Example
// C program to check given number is odd or even number
#include<stdio.h>
int main()
{
int number=0;
printf("enter a number:");
scanf("%d",&number);
if(number%2==0)
{
printf("%d is even number",number);
}
else
{
printf("%d is odd number", number);
}
printf(“End of Program");
}
Output1:
Enter a number:4
4 is even number
Output2:
Enter a number:11
11 is odd number

16. IF( ) … else ….STATEMENT Example
// C Program to check whether a person is eligible to vote or not.
#include <stdio.h>
int main()
{
int age;
printf("Enter your age?");
scanf("%d",&age);
if(age>=18)
{
printf("You are eligible to vote...");
}
else
{
printf("Sorry ... you can't vote");
}
}
Output1:
Enter your age?18
You are eligible to vote...
Output2:
Enter your age?13
Sorry ... you can't vote

17. IF( ) … else ….STATEMENT Example
// Program to check whether an integer is positive or negative
// This program considers 0 as a positive number
#include <stdio.h>
int main() {
int number;
printf("Enter an integer: “); scanf(“%d”, &number);
if (number >= 0)
{
printf("You entered a positive integer: %d”, number );
}
else
{
printf(" "You entered a negative integer : %d”, number );
}
cout << "This line is always printed.";
}
Output1:
Enter an integer: 4
You entered a positive integer: 4.
This line is always printed.
Output2:
Enter an integer: - 4
You entered a negative integer: -4.
This line is always printed.

18. LOGICAL OPERATORS IN C

19. LOGICAL OPERATORS IN C
Note: a and b are both relational expression here

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

21. Here, if the condition 1 is false then it
skipped tostatement 3.
But if the condition 1 is true, then it
testscondition 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,
NESTING OF IF…..ELSE STATEMENTS

22. Program
/*Selecting the largestof threevalues*/
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

23.  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 else if ladder

24. The else if ladder
 When a multipathdecision is involved then we use else if ladder.
 A multipath decision is a chain of ifs in which the statement associated
witheach else is an if.
 Ittakes the following general form,

25.  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 else if ladder

26. THE SWITCH STATEMENT
⚫Switch statement is used for complex programs when
the numberof 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
thatcase is executed.

27. Switch case flowchart

28. SWITCH STATEMENT
⚫ Thegeneral form of switch statement is
switch(expression)
{
casevalue-1:
block-1 break;
casevalue-2:
block-2 break;
…….
…….
default: default-block break;
}
statement-x;

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

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

31. UNCONDITIONAL STATEMENTS - THE GOTO STATEMENT
C supports the goto statement to
branchunconditionally from one point of the
program toanother.
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 byacolon.

32. DECISION MAKING AND LOOPING
 In looping, a sequence of statements are executed until some
conditions for terminationof the loopare satisfied.
 In looping, a sequence of statements are executed until some
conditions for terminationof the loopare 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.

33. 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.

34. Loops In C
⚫The C language provides for three loop constructs for
performing loopoperations.
⚫Theyare:
The whilestatement
The dostatement
The forstatement

35. THE WHILE STATEMENT
⚫The basic formatof the while statement is
while(testcondition)
{
bodyof the loop
}
⚫ The while isan entry–controlled loop statement.
⚫ The test-condition is evaluated and if the condition is true, then the
bodyof 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 onceagain.
⚫ 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.

36. Example of WHILE Loop
Bodyof the loop test
condn?
while(testcondition)
{
bodyof the loop
}
sum = 0;
n = 1;
while(n <= 10)
{
sum = sum + n* n;
n = n + 1;
}
printf(“sum = %d n”,sum);

37. While loop

39. 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);

40. 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(“Inputa numbern”);
number= getnum();
}
while(number> 0);

41. Difference between While( ) loop and Do….while() loop

45. THE FOR STATEMENT
⚫The for loop is another entry-controlled loop that
provides a more concise loop control structure
⚫Thegeneral form of the for loop is
for(initialization ; test-condition ; increment/Decrement)
{
body of the loop
}

46. THE FOR STATEMENT
for(initialization ; test-condition ; increment/Decrement)
{
body of the loop
}

47. Cont..
⚫ The execution of the forstatement isas follows:
 Initialization of the control variables is done first.
 Thevalue of thecontrol 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
statementthat 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
perthecondition.

48. Cont..
⚫Eg 2)
sum = 0;
for(i = 1; i < 20; ++i)
{
sum =sum + i;
printf(“%d %d n”,sum);
}
for(initialization ; test-condition ; increment/Devrement)
{
bodyof the loop
}

49. For Statement
⚫Eg 1)
for(x = 0; x <= 9; x = x + 1)
{
printf)”%d”
,x);
}
printf(“n”);
⚫ The multiplearguments in the incrementsectionare possible
and separated by commas.

50. Nesting of For Loops
⚫C allowsone forstatementwithin anotherfor
statement.

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

52. JUMPS IN LOOPS
 C permits a jump from one statement to another within a
loop as well as the jumpoutof a loop.
Jumping outof a Loop
 An early exit from a loop can be accomplished by using the
break statementor thegoto statement.
 When the break statement is encountered inside a loop, the
loop is immediately exited and the program continues with
thestatement 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.

53. Skipping a part of a Loop
⚫Like the break statement, C supports another similar
statementcalled thecontinue 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,
FOLLOWING STATEMENTS AND CONTINUE WITH
ITERATION”.
⚫The formatof thecontinue statement is simply
“SKIP THE
THE NEXT
continue;

54. Bypassing and continuing I Loops

55. 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