Loops

Loops in a programming is used to iterate the statements or run part of the program several times.

Types of Loops:

For loop
while loop
do-while loop

1.For loop

For loops are used when you have a block of code which you want to repeat a fixed number of times.

syntax:

1. for(initilization; condition; inc/dec)
{// loop body start

} // loop body ends

initilization - initializes variable and executed only once.
condition -if true, the body of for loop is executed if false, the for loop is terminated.
inc/dec - increases or decrease the value of initialized variables and again checks the condition.

Example 1️⃣ :

#include <iostream>
using namespace std;

int main() {

    int i;
    for(i=0;i<5; i++)
    {
      cout<<"Hello \n";
    }
     return 0;
}

Output :

Hello
Hello
Hello
Hello
Hello

Explanation :

Line 6 : Declare i variable.
Line 7 : for(i=0;i<5; i++) for is keyword, i=0 initialize i, i<5 condition to check, i++ increase value one by one.
Line 8 : loop body starts.
Line 9 : print Hello using cout.
Line 10 : loop body ends.

Example 2️⃣ : Reverse

#include <iostream>
using namespace std;

int main() {

    int i;
    for(i=4;i>0; i--)
    {
      cout<<"Hello \n";
    }
     return 0;
}

Output :

Hello
Hello
Hello
Hello

Explanation :

Line 6 : Declare i variable.
Line 7 : for(i=4;i>0; i--) for is keyword, i=4 initialize i, i>0 condition to check, i-- decrease value one by one.
Line 8 : loop body starts.
Line 9 : print Hello using cout.
Line 10 : loop body ends.

Example 3️⃣ : Reverse

#include <iostream>
using namespace std;

int main() {

    int i;
    for(i=4;i>0; i--)
    {
      cout<<i<<"\n";
    }
     return 0;
}

Output :

4
3
2
1

Explanation :

Infinite Loop:

loops condition is always true .
it always runs because stoppping condition never occurs .

Example 1️⃣ :

#include <iostream>
using namespace std;

int main() {

    int i;
    for(i=1;i>0; i++)
    {
      cout<<i<<"\n";
    }
     return 0;
}

Output :

1
2
3
.
.
.
.
.
infinite

Explanation :

Line 6 : Declare i variable.
Line 7 : for(i=1;i>0; i++) for is keyword, i=1 initialize i, i>0 condition to check, i++ increase value one by one.
Line 8 : loop body starts.
Line 9 : print i variable using cout.
Line 10 : loop body ends.

Practice Program

Example 2️⃣ : WAP to print all even numbers upto n

#include <iostream>
using namespace std;

int main() {

    int n;
    cout<<"Enter value of n: ";
    cin>>n;
    for(i=2;i<=n; i+2)
    {
      cout<<i<<"\n";
    }
     return 0;
}

Output :

Enter value of n: 20
2
4
6
8
10
.
.
.
20

Explanation :

Line 6 : Declare n variable.
Line 7 : enter value of n: from user.
Line 9 : for(i=2;i<=n; i+2) for is keyword, i=2 initialize i, i<=n condition to check, i+2 increase value by two.
Line 10 : loop body starts.
Line 11 : print i variable using cout.
Line 12 : loop body ends.

Example 3️⃣ : WAP to print all even numbers upto n

#include <iostream>
using namespace std;

int main() {

    int n;
    cout<<"Enter value of n: ";
    cin>>n;
    for(i=2;i<=n; i=i+2)
    {
        if(i%2 == 0)
        {
           cout<<i<<endl;
        }
    }
     return 0;
}

Output :

Enter value of n: 10
2
4
6
8
10

Example 4️⃣ :WAP to print sum of n numbers ?

#include <iostream>
using namespace std;

int main() {

    int n;
    cout<<"Enter value 0f n: ";
    cin>>n;

    int sum =0;
    for(i=1;i<=n; i++)
    {
        sum = sum + i;
    }
    cout<<"Sum : "<<sum;
     return 0;
}

Output :

Enter value of n: 5
Sum :15

Explanation :

Line 6 : Declare n variable.
Line 7 : enter value of n: from user.
Line 10 : initialize sum variable.
Line 11 : for(i=1;i<=n; i++) for is keyword, i=1 initialize i, i<=n condition to check, i++ increase value by one.
Line 12 : loop body starts.
Line 13 : sum = sum + i In sum variable assign value of sum + i ,
Line 14 : loop body ends.
Line 15 : print sum variable

Loops

Types of Loops:​

1.For loop

Infinite Loop:​

Practice Program​

Types of Loops:

Infinite Loop:

Practice Program