Nested loops

Nested Loops
• What is a nested loop?
• Types of nested loops
• Working of a nested loop
• Example Programs

What are nested loops?
• A nested loop is a loop
inside the body of
another loop.
• The nested loop is
known as the inner loop
and the loop in which it
is nested is known as the
outer loop
for ( int i=0; i< 3; i++)
{
for (int j = 0; j<3; j++)
cout<< j << “ “;
}
Outer loop
Inner loop
Outerloopbody
Innerloopbody

Types of Nested Loops
Nested for Nested while Nested do while Mixed

Nested for loop
for ( initialization; test; update) outer loop
{ //outer loop statements;
for( initialization; test; update) inner loop
{
//inner loop statements;
}
}

Nested while loop
while ( test) outer loop
while( test) inner loop
{
}
}

Nested do …. while loop
do outer loop
do inner loop
{
} while (test);
} while(test);

Working of nested loops : example 1
For each iteration of the outer loop, the inner loop is completely executed.
So for example for the following nested loop:
for(int i=0; i<3;i++)
for(int j=0; j<3;j++)
cout<<j<<“ ” ;
the statement, cout<<j<<“ ” ,will execute 3X3=9 times. For each iteration of
outer loop( i = 0, 1, 2) , inner loop will execute 3 times(j= 0, 1, 2).
Also note that there are no brackets. This is because both loops contain
single statements; outer loop contains inner loop and inner loop contains
single cout statement.

If the loop contains multiple statements then there is a need for brackets.
For the following nested loops:
for(int i=0; i<2;i++)
{ cout<<“n”;
for(int j=0; j<3;j++)
cout<<j<<“ ” ;
}
the statement, cout<<j<<“ ” ,will execute 2X3=6 times. For each iteration of outer
loop( i = 0, 1) , inner loop will execute 3 times(j= 0, 1, 2).
There are brackets in the above nested loop. This is because the outer loop
contains two statements; one cout<<“n” and the inner loop . The inner loop
contains single cout statement thus there are no brackets for inner loop.

If the loop contains multiple statements then there is a need for brackets.
For the following nested loops:
for(int i=0; i< 4;i++)
{ cout<<“n”;
for(int j=1; j<= 2;j++)
{cout<<j<<“ ” ;
cout<<“inner loop”;
}}
There are brackets in both the above nested loop. This is because the outer loop contains
two statements; one cout<<“n” and the inner loop . The inner loop contains two
statements 1.cout<<j<<“”and cout <<“inner loop “.
For each iteration of outer loop( i = 0, 1,2,3) , inner loop will execute 2 times(j= 1, 2). So
total no of times= 4X2=8

Working of Nested Loops
for(int i= 0 ; i< 2; i++)
{
cout<<“n”;
for(int j = 0; j<2; j ++)
cout<< j << “ ”;
}
1 2
3
4 5
6
8
7
1. STEP 1:The outer loop is initialized with value of i as 0
2. STEP 2: Value of i is tested, since the condition is true( i<2), the loop
is entered
3. STEP 3:A newline is displayed (cout<<“n”;). This is part of outer loop.
4. STEP 4 :The control goes to inner loop, where j is initialized with 0
5. STEP 5: Value of j is tested, j<2 is true, inner loop is entered
6. STEP 6: The statement cout << j << “”is executed, value of j is displayed
7. STEP 7: The value of j is incremented.
8. Now STEPs 5, 6 and 7 are repeated till the condition ,j<2,
becomes false.
9. When value of j is 2, control comes out of inner loop.
8. STEP 8: Now the control goes to outer loop update statement,
i is incremented.
9. STEPs 2 – 7 are repeated. The steps are repeated for value of i = 1
This continues till value of i becomes 2. Then the outer loop is
terminated.

Working of nested loops
Output:
0 1
0 1
for(int i= 0 ; i< 2; i++)
{
cout<<“n”;
for(int j = 0; j<2; j ++)
cout<< j << “ ”;
}
0
i
1
0
1
j
0
1
i
1 2
3
6
4 5 7
8
2
2 2
i

Program: To print the pattern
#include<iostream.h>
void main()
{
for( int x = 1; x < 3; x ++)
{
for ( int y = 1; y <= x; y ++)
cout<<y <<”t”;
cout<< ”n” ;
}}
1
1 2
1 2 3
Explanation
1.Outer loop : 1st Iteration x=1
1.1 Inner Loop : 1st Iteration,y=1 cout<<y<<“t
Increment y , y=2, check y<=x=false Inner loop over
2. Outer loop :2nd Iteration x=2
2.1 Inner loop : 1st Iteration ,y=1 cout<< y<<“t”
2.2 Inner loop : 2nd Iteration, y=2 cout<<y<<“t”
3. Outer loop :3rd Iteration x=3
3.1 Inner loop : 1st Iteration y=1, cout<<y<<“t”
3.2 Inner loop : 2nd Iteration, y=2, cout<<y<<“t”
3.3 Inner loop : 3rd Iteration , y = 3, cout<<y<<“t”
increment x, x= 3, outer loop over
Output

Program :Program to find the divisors of numbers
entered.
#include<conio.h>
void main()
{ int n, k;
cout<< “Enter the number of integers :”;
cin >> n;
for( int i = 0; i < n; i ++)
{ cout<< “Enter the number of whose divisor are to be found”;
cin >> k;
cout << “n The divisor are :”<<”n”;
for ( int j = 1; j <= k/2; j ++)
if( k%j == 0)
cout<< j <<”t”;
}
EXPLANATION:
The outer loop keeps track of the
number of integer a user inputs.
The inner loop calculates and displays
its divisors
Enter the number of integers : 2
Enter the number whose divisor is to be found : 6
The divisors are :
1 2 3
Enter the number whose divisor is to be found : 15
The divisors are :
1 3 5
Output

Program : Display the multiplication table of a number till the
user wishes
#include<conio.h>
void main()
{
int num, l;
char ch;
do
{cout<<”Enter a number whose multiplication table is to be displayed:
”;
cin>>num;
cout<<”Enter the limit of upto which table is to be displayed :”;
cin>>l;
int i = 1;
while( i <= l){
{
cout<<num<<”X”<< i <<”=”<<num*i <<”n”;}
cout<<”Do you wish to continue (Y/N)”<<”n”;
cin>>ch; } while(ch!=’n’||ch!=’N’);}}
Enter a number whose multiplication table is to
be displayed: 8
Enter the limit upto which table is to be
displayed : 4
8X1=8
8X2=16
8X3=24
8X4=32
Do you wish to continue(Y/N)
Y
Enter a number whose multiplication table is to
be displayed: 6
Enter the limit upto which table is to be
displayed : 5
6X1=6
6X2=12
6X3=18
6X4=24
6X5=30
Do you wish to continue(Y/N)
N
Output

Nested loops

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