The document discusses various control structures in C language that are used to control the flow of execution in a program. It explains the three types of execution flow as sequence, selection, and repetition. Under selection it covers if, if-else, if-else-if, switch statements. Under repetition it covers while, do-while, for loops. For each control structure, it provides syntax, examples and explanations.

1. Problem Specification

2. • Control Structure
• if Statement
• if-else Statement
• if-else-if Statement
• Nested if Statement
• Switch Statement
• Difference between if-else-if and switch Statement
• While Loop
• Do while Loop
• For Loop
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Topics
Contents

3.  Control structures control the flow of execution in a program
 The control structures in C language are used to combine individual instruction into a single logical unit
 The logical unit has one entry point and one exit point
 There are three kinds of execution flow:
• Sequence
• Selection
• Repetition
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4. Sequence
 Executes the statements in the same order in which they are written in the program
Entry point
Exit point
Flowchart
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5. Selection
 A control structure which chooses alternative to execute
 Executes a statement or set of statements based on a condition
 Also called decision-making structure or conditional
structure.
 Different types of selection structures in C language:
 If
 if-else
 if-else-if
 switch
Flowchart
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Exit point
Entry point

6. Repetition
 A control structure which executes a statement or set of statements repeatedly for a specific number of times
 Also called iteration structure or loop
 Different types of loops available in C language:
 while loop
 do-while loop
 for loop
Entry point
Exit point
Flowchart
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7.  The if statement is the primary selection control structure
 It is used to execute or skip a statement or set of statements by checking a condition
 The condition is given as a relational expression. e. g marks >=40
Syntax / General Form
The syntax of if statement for single statement:
if (condition)
statement;
The syntax for compound statements:
if (condition)
{
statement 1;
statement 2;

statement N;
}
if is a keyword in C
language. It is always
written in lowercase.
Block of statements
inside the braces is
called the body of the if
statement. If there is
only 1 statement in the
body, the { } may be
omitted.
Do not place ; after (condition)
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8. If Programs
#include <iostream>
using namespace std;
int main() {
int marks;
// Taking input for marks
cout << "Enter your marks: ";
cin >> marks;
// Checking if marks are 40 or more
if (marks >= 40) {
cout << "Congratulations! You have passed." << endl;
}
return 0;
}
Output:
Enter your marks: 65
Congratulations! You have passed.

9. #include <iostream>
#include <cmath>
using namespace std;
int main() {
int num1, num2;
// Input for the first number
cout << "Enter the first number: ";
cin >> num1;
// Input for the second number
cout << "Enter the second number: ";
cin >> num2;
// Checking if the second number is the square of the first number
if (num2 == (num1 * num1)) {
cout << num2 << " is the square of " << num1 << "." << endl;
}
return 0;
}
Output:
Enter the first number: 5
Enter the second number: 25
25 is the square of 5.

10.  The simplest selection structure but it is very limited in its use
 Statement or set of statements is executed if the condition is true
 But if the condition is false then nothing happens (no alternate action is performed)
 A user may want to:
Execute one statement or set of statements if the condition is true
Execute other statement or set of statements if the condition is false
 In this situation, simple if statement cannot be used effectively
 Solution  ‘if-else’ structure can be used to handle this kind of situation effectively
Example
A program should display Pass! if the student gets 40 or more marks
It should display Fail! if the student gets less than 40 marks
Simple if statement cannot be used to handle this situation
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11.  Used to make two-way decisions
 It executes one block of statement(s) when the condition is true and the other when it is false
 In any situation, one block is executed and the other is skipped
 Both blocks of statement can never be executed
 Both blocks of statements can never be skipped
Syntax / General Form
The syntax of if-else statement for single and compound statements:
Condition
Statement
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cout<<“Number are equal”;
cout<<“Number are different”;

12. If-else Programs
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#include <iostream>
using namespace std;
int main() {
int number;
// Input for the number
cout << "Enter a number: ";
cin >> number;
// Checking if the number is even or odd using if-else structure
if (number % 2 == 0) {
cout << number << " is even." << endl;
} else {
cout << number << " is odd." << endl;
}
return 0;
}
Output:
Enter a number: 7
7 is odd.

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#include <iostream>
using namespace std;
int main() {
int year;
// Input for the year
cout << "Enter a year: ";
cin >> year;
// Checking if the year is a leap year using if-else structure
if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
cout << year << " is a leap year." << endl;
} else {
cout << year << " is not a leap year." << endl;
}
return 0;
}
Output:
Enter a year: 2024
2024 is a leap year.

14.  It is used when there are many options and only one block of statements should be executed on the basis of
a condition
Working of if-else-if
 The condition 1 is evaluated and the first block of statements is executed if the condition 1 is true
 The condition 2 is evaluated if the condition 1 is false. The second block of statements is executed if the
condition 2 is true
 The block of statements after the last else is executed if all conditions are false
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15. if-else-if Programs
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#include <iostream>
using namespace std;
int main() {
int number;
// Input for the number
cout << "Enter a number: ";
cin >> number;
// Checking if the number is positive, negative, or zero using if-else-if structure
if (number > 0) {
cout << "The number is positive." << endl;
} else if (number < 0) {
cout << "The number is negative." << endl;
} else {
cout << "The number is zero." << endl;
}
return 0;
}
Output:
Enter a number: -8
The number is negative.

16.  An if statement within an if statement is called nested if statement
Syntax / General Form
Working of Nested if
 the condition of outer if is evaluated first. If it is true, the control enters the inner if block
 If the condition is false, the inner if is skipped and control directly moves to the else part of outer if
 If outer if is true, the control enters the inner if statement
 The inner if evaluated according to simple if statement
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17. Copyright @ IT Series
Write a program that input three number. determine whether numbers are equal or not
using nested if structure.
#include <iostream>
using namespace std;
int main() {
int num1, num2, num3;
// Input for three numbers
cout << "Enter three numbers: ";
cin >> num1 >> num2 >> num3;
// Checking if numbers are equal using nested if structure
if (num1 == num2) {
if (num2 == num3) {
cout << "All three numbers are equal." << endl;
} else {
cout << "First two numbers are equal, but the third number is different." << endl;
}
} else {
cout << "The numbers are not all equal." << endl;
}
return 0;
}
Output:
Enter three numbers: 5 5 5
All three numbers are equal.

18.  Select one of several alternatives when selection is based on the value of a single variable or an expression
 In C, the value of this expression may be of type int or char
 The switch statement is a better way of writing a program when a series of if-else-if occurs
Syntax / General Form
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19. Rules of using switch case in C/C++ program
• The case label must integer or character
• Each case label must be unique
• A switch statement can have only one default label
• The default label can be used anywhere in switch statement
• The case label must end with colon. The default label is optional
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#include <iostream>
using namespace std;
int main() {
int day;
// Input for the day of the week (1-7)
cout << "Enter a number corresponding to a day of the week (1-7): ";
cin >> day;
// Using switch statement to display the day of the week
switch (day) {
case 1:
cout << "Monday" << endl;
break;
case 2:
cout << "Tuesday" << endl;
break;
case 3:
cout << "Wednesday" << endl;
break;
case 4:
cout << "Thursday" << endl;
break;
case 5:
cout << "Friday" << endl;
break;
case 6:
cout << "Saturday" << endl;
break;
case 7:
cout << "Sunday" << endl;
break;
default:
cout << "Invalid input! Please enter a number between 1 and 7." <<
endl;
break;
}
return 0;
Output:
Enter a number corresponding to a day of the week (1-7): 3
Wednesday

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21. Loop
 The control structure that executes a statement or set of statements repeatedly is called loop.
 Loops are also known as iteration or repetition structure
 Loops are basically used for two purposes:
 They are used to execute a statement or number of statements for a specified number of
times
 Example: A user may display his name on screen for 10 times
 The loops are also used to get a sequence of values
 Example: A user may display a set of natural numbers from 1 to 10
 There are three types of loops available in C:
 while loop
 do-while loop
 for loop

22.  while loop is the simplest loop of C
 It executes one or more statements while the given condition remains true
 It is useful when the number of iterations is not known in advance
Syntax
 Condition is evaluated:
 if it is true, the statement(s) are executed, and then condition is evaluated again
 if it is false, the loop is exited
An iteration is
an execution of
the loop body.
while is a
keyword. It is
always written in
lowercase.
Loop body
Don’t put ; after (condition)
while is a pretest
loop (the condition
is evaluated before
the loop executes)
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Flowchart

23. while Loop Example
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int n;
n = 1;
while(n<=5)
{
printf(“Pakistann");
n++;
}
 Produces output:
Counter Variable
 A variable that is incremented or decremented each time a loop iterates
 It can be used to control the execution of the loop (as a loop control variable)
 It must be initialized before entering loop
 It may be incremented/decremented either inside the loop or in the loop test
n++; is the same as n= n + 1;
Don’t put ; after (condition)
Loop body
while is a pretest
loop (the condition
is evaluated before
the loop executes)
cout<<“Pakistann”;

24. Infinite loop
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 The loop must contain code to allow the condition to eventually become false so the loop can be exited
 Otherwise, you have an infinite loop
Example
int n; n = 1;
while(n<10)
cout<<n<<"t";
Infinite loop because n is always < 10
A loop that does not
stop is known as an
infinite loop

25.  This loop executes one or more statements while the given condition is true
 In this loop, the condition comes after the body of loop
 The loop body always executes at least once
Syntax:
 Execution continues as long as the condition is true; the loop is exited when the condition becomes false
 ; after (condition) is also required
 The loop executes at least once even if the condition is false in the beginning
An error occurs if the semicolon
is not used at the end of the
condition.
Loop body
do-while is a post
test loop (condition
is evaluated after
the loop executes)
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26. do-while Loop Example
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int n;
n = 1;
do
{
cout<<“Welcome to Cn”;
n++;
}
while(n<=5);
Loop body
do-while is a post
test loop (condition
is evaluated after
the loop executes)
Condition

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cout<<n<<“t”;
cout<<n<<“t”;

28.  It is a pretest loop that executes one or more statements for a specified number of times
 This loop is also called counter-controlled loop
 It is useful with counters or if precise number of iterations is known
Syntax / General Form Example
for (initialization; condition; increment/decrement)
{
statement 1;
statement 2;


statement N;
}
Flowchart
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cout<<“Welcom to C++n”;

29.  You can define variables in initialization code
for (int n=1; n <= 5; n++)
 Can omit initialization if already done
int n = 1;
for (; n <= 5; n++)
 Can omit update if done in loop body
for (n = 1; n<= 5;)
n++;
 The condition in for loop is mandatory. It cannot be omitted
int n=1;
for (;n<= 5;)
n++;
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