This document provides an overview of control structures in the C programming language. It discusses selection statements like if, if-else and switch statements that allow conditional execution of code. It also covers iteration statements like for, while and do-while loops that allow repetitive execution. Additionally, it explains jump statements like break, continue, goto and return that change the flow of control.

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Control Structures in C

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4. Flow of control
• Unless specified, the order of statement
execution is linear: one statement after another
in sequence
• A control structure is any mechanism that
departs from the default straight-line
execution.

5. 2
1
3

6. Selection statements
• Used to choose which statement to be executed next
• Therefore they are sometimes called conditional statements
• Conditional statements give us the power to make basic
decisions
• The C conditional statements are the:
– if statement
– if-else statement
– switch statement

7. The if Statement
The if statement has the following syntax:
if ( condition )
statement;
• if is a C reserved keyword.
• The condition must be a boolean expression. It is evaluated to
either true or false.
• If the condition is true, the statement is executed.
• If it is false, the statement is skipped.

8. The if-else Statement
• If the condition is true, statement1 is executed; if
the condition is false, statement2 is execute
if ( condition )
statement1;
else
statement2;

9. Consider the following example,
int grade=76;
if ( grade >= 60 )
printf( "Passedn");
else
printf( "Failedn");
The above code will produce an
output:
Passed
Since the true statement only executes

10. • An if statement which is within another
if or else is called nested if.
• Braces can be used to specify the if
statement to which an else clause
belongs
Nested if statements

11. Syntax of nested if:
if(condition1)
{
if(condition2)
do this;
else //this else with condition2
{
do this;
and this;
}
}
else //this else with condition1
do this;
Note that in C an else statement always refers to the
nearest if that is within the same block of else.

12. An example for nested if:
if(avg>=90)
printf("Student %s gets an A grade",name);
else if(avg>=80 &&avg<90)
printf("Student %s gets a B grade",name);
else if(avg>=70 &&avg<0)
printf("Student %s gets a C grade",name);
else if(avg>=60 &&avg<70)
printf("Student %s gets a D grade",name);
else if(avg<60)
printf("Student %s failed");
Nested if (contd…)

13. The Switch statement
• The switch statement provides another way to
decide which statement to execute next
• The switch statement evaluates an expression, then
attempts to match the result to one of several
possible cases
• Each case contains a value and a list of statements
• The flow of control transfers to statement associated
with the first case value that matches

14. • Often a break statement is used as the last statement
in each case's statement list
• A break statement causes control to transfer to the
end of the switch statement
• If a break statement is not used, the flow of control
will continue into the next case
• Sometimes this may be appropriate, but often we want
to execute only the statements associated with one
case
The Switch statement(Contd…)

15. • A switch statement can have an optional
default case
• If the default case is present, control will
transfer to it if no other case value matches
• If there is no default case, and no other
value matches, control falls through to the
statement after the switch
The Switch statement(Contd…)

16. • The expression of a switch statement must result in
an integral type, meaning an integer (byte, short,
int,) or a char
• It cannot be a floating point value (float or double)
• The implicit test condition in a switch statement is
equality
• You cannot perform relational checks with a switch
statement
The Switch statement(Contd…)

17. The general syntax of a switch statement is:
switch ( expression )
{
case value1 :
statement-list1
case value2 :
statement-list2
case value3 :
statement-list3
default:
statement
}
switch
and
case
are
reserved
words
If expression
matches value2,
control jumps
to here
The Switch statement(Contd…)

18. switch (option)
{
case 'A':
aCount++;
break;
case 'B':
bCount++;
break;
case 'C':
cCount++;
break;
default:
otherCount++;
break;
}
The Switch statement(Contd…)
An example for switch statement:

19. Iteration Statements
• Also known as loops
• It allow a set of instructions to be executed
until a certain condition is met.
• The loop structures available in C are:
• For loop
• While loop
• Do while loop

20. The for Loop
• The syntax of for statement in C:
for (initialization expression;loop repetition condition;update expression)
{
statement
}
• The initialization expression set the initial value of the loop
control variable.
• The loop repetition condition test the value of the loop control
variable.
• The update expression update the loop control variable.

21. Nested Loops
• Nested loops consist of an outer loop with one or more
inner loops.
• e.g.,
for (i=1;i<=100;i++){
for(j=1;j<=50;j++){
…
}
}
• The above loop will run for 100*50 iterations.
5-22
Inner loop
Outer loop

22. For loop: An example
/*For loop to print even numbers below 100*/
for(i=2;i<100;i=i+2)
{
printf("%d,",i);
}

23. The While loop
• The syntax of do-while statement in C:
do
statement
while (loop repetition condition);
• The statement is first executed.
• If the loop repetition condition is true, the
statement is repeated.
• Otherwise, the loop is exited.

24. An Example of the do-while Loop
/* Find even number input */
do{
printf(“Enter a value: ”);
scanf(“%d”, &num);
}while (num % 2 !=0)
5-25
This loop will repeat if the user
inputs odd number.

25. Jump Statements
• Also called unconditional branching.
• It means transfer of control to a specified
statement.
• C has four statements that perform
unconditional branch
– Call/return
– Goto
– Break
– Continue

26. The return statement
• Used to return fro a function
• It returns to the point at which the function is
called.
• It can have a value with it.
• General form: return (expression);
• The expression is optional
• Function can have more than one return
statement, but will return at the first return
statement

27. The goto statement
• Allows to transfer control to any other
statement in the function.
• General form
label:statement
goto label;

28. The break statement
• It can be used to terminate a case in switch
statement.
• Can used to force immediate loop termination
by checking a condition

29. • Here, loop will terminate when i=10
for(i=0;i<=100;i++)
{
if(i==10)
{
break;
}
printf(“%d”,i);
}

30. The Continue Statement
• It allows to skip the current iteration and
hence wont run the remaining statements in
the loop.

31. for(i=0;i<=100;i++)
{
if(i==10)
{
break;
}
printf(“%d”,i);
}
• Here, loop will skip the printf statement when i=10 and incement i to 11

32. thank you

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