c-programming-class 2

8/14/2019 C-Programming-Class 2

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Session 02

Control Statements & Storage

Specifiers


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Session Objectives

To learn about different types of Control

Statements

To learn about different Storage ClassSpecifiers


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Session Topics

Decision Structures if statement, if-else statement,

nested if statement

The switch statement

Repetition or Iteration structure - for statement,continue statement, nested loop, while loop

Storage class


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Decision making and Branching

To change the order of execution based on certain conditionsor repeat a group a statements until certain specifiedconditions are met.

Any expression can be used as a program statement by

following the expression with a ; (semicolon).

ANSI C has the following categories of statements Selection if, switch

Iteration for, do, while

Jump continue, break, goto, return Label case, default, (goto) label statement

Expression valid expression

Block { } (also called compound statements)


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C Control Structure Decision

{ . . . }Compound Statements

if - else switch - case

break

break


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C Control Structure Looping

The while loop keeps repeating an action until an associated test

returns false. This is useful where the programmer does not know

in advance how many times the loop will be traversed.

The do while loops is similar, but the test occurs after the loop

body is executed. This ensures that the loop body is run at least

once.

The for loop is frequently used, usually where the loop will be

traversed a fixed number of times. It is very flexible, and novice

programmers should take care not to abuse the power it offers.


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C Control Structure Looping

n - times

while do-while for


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The if else Statement

Structure if (expression)

statement_1

else

statement_2

The elsepart is optional

The expression is evaluated: ifexpression is TRUE(I.e. non zero)

thenstatement_1. Ifexpression isFALSE(i.e. zero) then

statement_1 is executed if present. For multiple ifs, the else

goes with the closest ifwithout an else condition.


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The if else Statement- Examples

#include int

main()

{

int b;

printf("Enter a value:");

scanf("%d", &b);

if (b < 0)printf("The value is

negative\n");

else if (b == 0)

printf("The value is

zero\n");

else

printf("The value is

positive\n");

return 0;

}


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The switch-case Statement

Multiple branch selection statement

Tests the value of an expression against a list of integer or char

constants

When a match is found, then statement associated with that

constant is executed.Structure switch (expression)

{

case I1: statements;



case In: statements;

default: statements; // optional

}


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The switch-case Statement contd

Operation: the expression is evaluated; then execution continues

at the statements following the case statement that matches the

result or after the label default if there are no matches. If the

defaultcase does not exist, then execution continues after the last

case statement.

Execution continues through remaining cases in the switch

structure unless the breakinstruction is encountered. If a breais encountered, then execution continues after the presentswitch-

case instance.


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The while Statement

Structure while(expression)statement;or

while(expression){

statement_1;

statement_2;}

The while StatementExample

while (a < b)

{

printf("%d\n", a);

a = a + 1;}

* Operation: expression is evaluated and ifTRUEthenstatement(or

statement_1 and statement_2) is executed. The evaluation andexecutions sequence is repeated until the expression evaluates to be

FALSE. If the expression is initiallyFALSEthenstatementis not

executed at all.


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Understanding a while loop

b=1;

While(b


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b=1;

While(b


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b=1;

While(b


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The do-while Statement

Structure do

{

statement;

} while(expression);

Operation: Similar to the whilecontrol except that

statement is executed before the expression is

evaluated. This guarantees that statementis always

executed at least one time even if expression is

FALSE. do {printf("%d\n", a);

a = a + 1;

} while (a < b);


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The for Statement

Structure: for(expr1; expr2; expr3)

{

statement;}

Operation: The for loop in C is simply a shorthand way of expressing a

while statement:expr1;while(expr2){

statement;

expr3} The comma operator lets you separate several different statements in

the initialization and increment sections of the for loop (but not in thetest section).


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Auxiliary Control Statements Break Causes the innermost control structure to be exited

immediately. Execution continues with the statement immediately

following the control structure just exited.

Continue Causes immediate execution of the next loop to begin.

Goto - Rumour has it that the goto statement should be avoidedbecause the program flow will jump all over the place, generating

what's known as SPAGHETTI CODE! No harm in using it in the

most simplest of programs though, but don't make a habit of using

it!! The goto keyword is followed by a label, which is basically some

identifier placed elsewhere in the program - like a hyperlink the

points to a place on the same web page.


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Looping: A Real Example

Let's say that you would like to create a program that prints a

Fahrenheit-to-Celsius conversion table. This is easily

accomplished with a for loop or a while loop:

#include

int main(){

int a;a = 0;while (a


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C Errors to Avoid

Putting = when you mean == in an if or while statement

Forgetting to increment the counter inside the while loop - If you

forget to increment the counter, you get an infinite loop (the loop never

ends). Accidentally putting a ; at the end of a for loop or if statement so that

the statement has no effect - For example:

for (x=1; x


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Storage Class Specifiers

C has four kinds of storage classes Automatic

Register

Static

External

Storage class is used to denote to the compiler where memory is to beallocated for variables

Storage class tells, what will be the initial value of the variable, if the

initial value is not specifically assigned.(i.e the default initial value).

Storage class informs the compiler thescope of the variable.Scope refers

to which functions the value of the variable would be available. Storage class informs the compiler the life of the variable. Life refers to

how long would the variable exist.


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Automatic Storage Class

All variables declared within a function are called localvariables, by

default belong to the automatic storage class.

Till the control remains within

the block in which it is

defined

Life

Local to the block in

which the variable is

defined

Scope

Garbage ValueDefault Initial Value

MemoryStorage


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Example for Automatic Storage Class

Main(){

auto int j=1;

{

auto int j=2;

{

auto int j=3;

printf(%d\n,j);

}

printf(%d\n,j);

}

printf(%d\n,j);

}

Output:

3

2

1


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Example for Register Storage Class

main()

{

register int i;

for(i=1;i


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Example for Static Storage Class

main()

{

function();

function();

function();

}function()

{

static int i=1;

printf(%d\n,i);

i=i+1;

}

Output

1

2

3

main()

{

function();

function();

function();

}

function()

{

auto int i=1;

printf(%d\n,i);

i=i+1;

}

Output

1

1

1


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External Storage Class

Variables declared outside functions have externalstorage class

As long as the programs

execution doesnt come to an

end

Life

GlobalScope

ZeroDefault Initial Value

MemoryStorage


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Example for External Storage Class

int i;

main()

{

printf(i=,i);

increment();

increment();

decrement();

decrement();}

increment()

{

i=i+1;

printf(On incrementingi = %d\n,i);

}

decrement()

{

i=i-1;

printf(On incrementing

i=%d\n,i);

}

Output:

i=0On incrementing i=1

On incrementing i=2

On decrementing i=1

On decrementing i=0


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Summary The different decision structure are if statement, if else statement,

multiple choice else if statement. The while loop keeps repeating an action until an associated test returns

false.

The do while loops is similar, but the test occurs after the loop body isexecuted.

The for loop is frequently used, usually where the loop will be traverseda fixed number of times.

Storage class is used to denote to the compiler where memory is to beallocated for variables

C has four kinds of storage classes

Automatic

Register

Static

External


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