# Flow of Control

Pseudo Code

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### Control Structures

There are three types of flow of control

• Sequential flow
• Selection or Conditional flow
• Iterative flow

### Sequential Flow

Steps of the algorithm is executed one by one in a sequence.

``````
statement 1
statement 2
statement 3
:
:
``````

Example
``````
Set sum = 0;
Set sum = x + y;
Print: sum;
``````

Note! Above instructions are executed step by step

### Selection or Conditional Flow

Selection flow are of three types

• Single Alternative
• Double Alternative
• Multiple Alternative

#### Selection Flow – Single Alternative

Single Alternative

``````
if expression then
statements
endif
``````

Example
``````
if x == 10 then
Print: “TEN”;
endif
``````

Note! If the expression is TRUE then the statements inside the body of the if is executed otherwise it is ignored.

#### Selection Flow – Double Alternative

Double Alternative

``````
if expression then
statement-A
else
statement-B
endif
``````

Example
``````
if x == 10 then
Print: “TEN”;
else
Print: “x is not TEN”;
endif
``````
Note! If the expression is TRUE then statement-A is executed otherwise statement-B is executed.

#### Selection Flow – Multiple Alternative

Multiple Alternative

``````
if expression-1 then
statement-1
else if expression-2 then
statement-2
:
:
else if expression-n then
statement-n
else
statement-last
endif
``````

Example
``````
if x == 1 then
Print: “ONE”;
else if x == 2 then
Print: “TWO”;
else if x == 3 then
Print: “THREE”;
else
Print: “x is not 1, 2 and 3”;
endif
``````

### Iterative Flow

Iterative flow are of three types

• for loop
• while loop
• do-while loop

#### Iterative Flow – for loop

Method 1

``````
for i = r to s by t do
statements
endfor
``````

Example
``````
for i = 1 to 5 by 1 do
Print: i;
endfor
``````

This will print 1 2 3 4 5

Method 2

``````
for (i = r; i <= s; i++)
statements
endfor
``````

Example
``````
for (i = 1; i <= 5; i++)
Print: i;
endfor
``````

This will print 1 2 3 4 5

#### How for loop works

``````
for i = r to s by t do
statements
endfor
``````

Algorithm in simple English
``````
1.	Initialize i = r   (PROCESS)
2.	Is i <= s  (DECISION)
if YES then
Execute statements
Calculate i + t and assign it to i
Repeat Step 2   (PROCESS)
else
Stop
``````

#### Iterative Flow – while loop

``````
while expression do
statements
endwhile
``````

Example
``````
Set i = 1;
while i <=5 do
Print: i;
Set i = i + 1;
endwhile
``````

This will print 1 2 3 4 5
Note! In while loop the expression is checked first and if it is TRUE then the statements inside the loop is executed otherwise it is ignored.

#### Iterative Flow – do-while loop

``````
do
statements
while expression
``````

Example
``````
Set i = 1;
do
Print: i;
Set i = i + 1;
while i <= 5
``````

This will print 1 2 3 4 5
Note! In case of do-while first the body of the loop is executed then the expression is checked. So with do-while you are guaranteed that the body will be executed at least once.

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