The document discusses loop control structures in C++. It explains the for, while, and do-while loops and provides examples. It also covers break, continue, return, and goto statements used to control program flow in loops.

1. Unit 3.2
Understand Loop Control Structures

2.  At the end of this presentation, students will be
able to:
◦ Understand looping control structures
◦ Describe the structure and working of for, while and
do-while loops
◦ Explain the need for break, continue, return and goto
statements

3.  Looping statements are used to :
◦ execute a set of instructions repeatedly, as long as the
specific condition is satisfied.
 The loop in C++ comes in 3 forms:
◦ for
◦ while
◦ do-while

4.  Syntax:
for(initialization;condition; incrementation/decrementation)
{
//loop statements
}
 Example:
for (i=0; i<5; i++)
{
cout << “n” << i ;
}

5.  initialization
◦ refer to initial value of loop counter
◦ carried out just once at the beginning of loop
 condition(expression)
◦ determined whether loop should continue
◦ if expression is false the loop will be terminate
 Incrementation/decrementation
◦ The initial value of the loop control variable is either
incremented or decremented each time the loop gets executed.

6.  The program LoopDemo.cpp illustrates the working
of a for loop.

7. #include<iostream>
using namespace std;
int main()
{
12345678910
int num;
for (num = 1; num <= 10; num++)
{
cout<<num;
}
return 0;
}

8.  There are a few patterns that you often need:
◦ To go from zero to some maximum – 1:
for (i = 0; i < max; ++i)
◦ Or, in the opposite direction:
for (i = max - 1; i >= 0; --i)
◦ Or To go from 1 to some maximum:
for (i = 1; i <= max; ++i)
◦ Or, in the opposite direction:
for (i = max; i > 0; --i)
 You might sometimes need a combination of elements from more
than one of these patterns, such as for (i = 0; i <= max; i++), but if
you write something unusual like this, make sure that it really is
what you want.

9.  Is a looping statement that enables you to repeat a set
of instructions based on a condition.
 If the condition is TRUE executes loop statement(s) in
the while block and executing its block until the
condition is FALSE.

10.  Syntax:
<initialise variable>
while(condition)
{
//loop statements
<Increment/decrement variable>;
}
 Expression is evaluated first
◦ If expression = TRUE then statement is executed
◦ If expression = FALSE then statement is bypassed

11.  Example:
while ((amount >0 && amount <=balance)
{
balance = balance – amount;
cout << “Please take your money” << amount;
cout << “This is your balance” << balance;
}

12.  Program While1.cpp illustrates the working of a
while loop.

13. #include<iostream>
using namespace std;
int main()
{ 1 3 5 7 9 11
int x=1;
while(x<=11){
cout<<x<<" ";
x=x+2;
}
return 0;
}

14.  The do-while loop is similar to the while loop.
 The difference only in the location where the
condition is checked. In do-while, condition is
checked at the end of loop.
Syntax
<initialise variable>
do
{
//loop statements
<Increment/decrement variable>;
} while(condition);

15.  Example
do {
cout << “Enter a value";
cin >> i;
if ( i<=0)
{
cout << “This is negative number";
}
} while (i>0);

16.  Program DoWhileDemo.cpp illustrates the
working of a do-while loop.

17. #include<iostream>
using namespace std;
int main() 1 3 5 7 9 11
{
int x=1;
do
{
cout<<x<<" ";
x=x+2;
}while(x<=11);
return 0;
}

18. while do-while
is no i = i+1
i > 10?
yes print i
print i
yes is
i > 10?
i = i+1
no

19.  Allow program controls to transfer from one part to
another part of program unconditionally
 4 types of jump statement:
◦ break
◦ continue
◦ return
◦ goto

20.  break
◦ The break statement causes termination of the loop
and transfers the control outside the loop.
◦ Program BreakDemo.cpp illustrates the use of break
statement.

21. #include<iostream>
using namespace std;
int main()
{ Entering into the loop
int i; 123456789
cout<<"Entering into the loopn"; Exiting out of the loop
for(i=1;i<20;i++)
{
if(i==10)
break; // exit from for loop
cout<<i<<" ";
}
cout<<"nExiting out of the loopn";
return 0;
}

22.  continue
◦ can only be used inside a loop.
◦ The continue statement will transfer the control to the
beginning of the loop.
◦ Program ContinueDemo.java illustrates the use of
continue statement.

23. #include<iostream>
using namespace std;
int main()
{
for(int i=1;i<=10;i++) 13579
{
if(i%2==0)
continue;
cout<<i<<" ";
}
return 0;
} The continue statement is executed when i%2==0. The continue
statement ends the current iteration so that the rest of the
statement in the loop body is not executed; therefore, i is printed
when i%2!=0.

24.  return
◦ terminate execution of current function AND return
value contained in the expression to the function that
invoked it.
 Example:
float CalcSum()
{
float sum;
sum = 15 + 20;
return sum;
}

25.  goto
◦ useful when you want to exit from a deeply nested
loop.
◦ control flow statement that causes the CPU to jump to
another spot in the code.
 Syntax
goto identifier ;
Example:
goto tryAgain;

26. #include <iostream>
#include <cmath>
using namespace std;
void main()
{
tryAgain: // this is a statement label
double number;
cout << "Enter a non-negative number: ";
cin >> number;
if (number < 0.0)
goto tryAgain; // this is the goto statement
cout << "The sqrt of " << number << " is " << sqrt(number) << endl;
}

27. In this presentation, you learnt the following:
 Looping statements are used to execute a set of
instructions repeatedly, as long as the specific condition
is satisfied.
 In C++, the looping control structures include
while, do-while and for.
 The break statement will transfer the control to
the statement outside the loop.

28.  The continue statement will transfer the control to
the beginning of the loop.
 The return statement will terminate execution of
current function and return the value.
 The goto may be necessary for exiting a loop from
within a deeply nested loop.

29. if (( x > 3) && (y < 7))
1. Consider the following
cout << "E";
code fragment: else
cout << "F";
cin >> x >> y; if (( x > 3) || (y < 7))
if ((x >= 3) && (y <= cout << "G";
7)) else
cout << "A";
cout << "H";
else
cout << "B";
if ((x >= 3) || (y <= 7)) ◦ What is the output
cout << "C"; produced if the user
else
cout << "D";
enters:
 3 and 7
 3 and 6
 4 and 7
 4 and 8

30.  3 and 7  4 and 7
ACFG
ACFH
 4 and 8
 3 and 6 BCFG
ACFG

31. 2. What is the output?
#include<iostream>
using namespace std;
int main()
{
int sum=0, item=0;
while (item<5) {
item++;
if(item==2)
continue;
sum+=item;
}
cout<<"The sum is"<<sum;
}

32. item<5
0 1 2 3 4
item++
1 2 3 4 5
if(item==2)
continue;
sum+=item;
1 4 8 13

33. 3. Write a program that can produce an output as
below by using the for, while, and do-while loop
8
6
4
2

34.  for loop
//solution 1
#include<iostream>
using namespace std;
int main()
{
for(int k=4; k>=1;k--)
cout<<k*2<<endl;
return 0;
}

35. //solution 2
#include<iostream>
using namespace std;
int main()
{
for(int k=8; k>=1;k--)
{
cout<<k<<endl;
k--;
}
return 0;
}

36.  while loop
//solution 1
#include<iostream>
using namespace std;
int main()
{
int k=4;
while(k>=1)
{
cout<<k*2<<endl;
k--;
}
return 0;
}

37. //solution 2
#include<iostream>
using namespace std;
int main()
{
int k=8;
while(k>=1)
{
cout<<k<<endl;
k--;
k--;
}
return 0;
}

38.  do-while loop
//solution 1
#include<iostream>
using namespace std;
int main(){
int k=4;
do{
cout<<k*2<<endl;
k--;
}while(k>=1);
return 0;
}

39. //solution 2
#include<iostream>
using namespace std;
int main(){
int k=8;
do{
cout<<k<<endl;
k--;
k--;
}while(k>=1);
return 0;
}