For Loop

In programming languages, the for loop is a control flow statement that executes a block of code several times. It iterates the same code repeatedly until the specified condition is true.

Here, we understand the purpose of for loop statement with a situation. Let's suppose we want to print a particular string like "I am learning for loop" 10 times. There is no requirement to write the same string every time. The easy way is to put the string in a for loop once and iterate the loop 10 times.

Points to remember

In C and C++, we can provide any values as true and false condition in conditional expression of for loop statement. Both language consider these values as Boolean and treats 0 as false and the rest of the values as true.
Unlike C and C++, Java throws an error on passing values in conditional expression of for loop statement as it has a Boolean type. It treats these values as integers.
JavaScript follows the similar for loop syntax as in Java with a difference that the three expressions enclosed within parenthesis are optional.
Unlike C and other languages, Python's for statement can be used to iterate the elements of any type of sequence (a list or a string).
Ruby uses do and end keywords in place of for loop open and close curly braces.
Swift performs the iteration in a range or collection. The range can be represented in two ways such as lowerBound...upperBound like 0...10 or lowerBound..
In rust, the for loop iterator is represented in the form of expression that contains the start and end position like 0...10. It includes the lower bound value and excludes the upper bound value.

Syntax in C/C++/C#/Java/JavaScript/PHP

for(initialization;condition;incr/decr){  
//code to be executed  
}  

Syntax in Python

for <variable> in <sequence>: 
//code to be executed

Syntax in Ruby

for variable [, variable ...] in expression [do]  
   code  
end  

Syntax in Swift/Rust

for variable in range {
   //code to be executed
}

Example 1 in C

#include <stdio.h>
int main () {
for(inti =1; i<=10; i++ ){
printf("%d\n", i);
   }
return 0;
}

Example 1 in C++

#include <iostream>
using namespace std;
int main()
{
for(inti=1;i<=10;i++)
    {
cout<<i<<endl;
}
return 0;
}

Example 1 in C#

using System;  
public class ForExample
    {  
public static void Main(string[] args)  
      {  
for(inti=1;i<=10;i++){    
Console.WriteLine(i);    
          }    
      }  
    }  

Example 1 in Java

public class ForExample {
public static void main(String[] args) {
for(inti=1;i<=10;i++)
  {
System.out.println(i);
  }
  }
}

Example 1 in JavaScript

<script>
for(i=1;i<=10;i++)
  {
document.writeln(i+"<br>")
  }
</script>

Example 1 in Python

fori in range(1, 11):
print(i)

Example 1 in Ruby

fori in 1..10 do   
putsi
end

Example 1 in PHP

<?php
for($i=1;$i<=10;$i++){  
echo "$i<br/>";  
}  
?>

Example 1 in Swift

fori in 1...10 {
print(i)
}

Example 1 in Rust

fn main() {
for x in 1..11 {
println!("{}", x); 
}
}

Example 2 in C

Let's see an example to print the sum of first 50 natural numbers in C.

#include <stdio.h>
int main()
{
int sum=0;
for(inti=1;i<=50;i++)
  {
sum=sum+i;
  }
printf("Sum=%d",sum);
return 0;
}

Example 2 in C++

#include <iostream>

using namespace std;

int main()
{
int sum=0;
for(inti=1;i<=50;i++)
  {
sum=sum+i;
  }
cout<<"Sum="<<sum ; 
return 0;
}

Example 2 in C#

using System;  
public class ForExample
    {  	
public static void Main(string[] args)  
      {  
int sum=0;
for(inti=1;i<=50;i++){    
sum=sum+i;
          }
Console.WriteLine("Sum="+sum);    
      }  
    }  

Example 2 in Java

public class ForExample {
public static void main(String[] args) {
int sum=0;
for(inti=1;i<=50;i++)
  {
sum=sum+i;
      }
System.out.println("Sum="+sum);
  }
}

Example 2 in JavaScript

<script>
var sum =0;
for(i=1;i<=50;i++)
  {
sum=sum+i; 
  }
document.writeln("Sum="+sum);
</script>

Example 2 in Python

sum=0;    
fori in range(1, 51):
sum=sum+i
print("Sum = "+str(sum))

Example 2 in Ruby

sum=0;
fori in 1..50 do   
sum=sum+i
end
puts "sum=#{sum}"

Example 2 in PHP

<?php
  $sum=0;
for($i=1;$i<=50;$i++){  
 $sum=$sum+$i;  
}  
echo "sum=$sum";  
?>

Example 2 in Swift

var sum=0;
fori in 1...50 {
sum = sum + i;
}
print("Sum=",sum)  

Example 2 in Rust

fn main() {
letmut sum=0;
fori in 1..51 {
sum=sum+i;
}
println!("Sum={}", sum); 
}

Output:

Sum=1275

Example 3 in C

#include <stdio.h>
int main()
{
inti,fact=1;  
intnum=5;   
for(i=1;i<=num;i++){    
fact=fact*i;    
  }    
printf("Factorial: %d",fact);  
return 0;
}

Example 3 in C++

#include <iostream>
using namespace std;
int main()
{
inti,fact=1;  
intnum=5;   
for(i=1;i<=num;i++){    
fact=fact*i;    
  }    
cout<<"Factorial: "<<fact;  
return 0;
}

Example 3 in C#

using System;  
public class ForExample
    {   
public static void Main(string[] args)  
      {  
inti,fact=1;  
intnum=5;   
for(i=1;i<=num;i++){    
fact=fact*i;    
  }    
Console.WriteLine("Factorial: "+fact);    
      }  
    }  

Example 3 in Java

public class ForExample{  
public static void main(String args[]){  
inti,fact=1;  
intnum=5;   
for(i=1;i<=num;i++){    
fact=fact*i;    
  }    
System.out.println("Factorial: "+fact);    
 }  
}

Example 3 in JavaScript

<script>
var fact=1;  
varnum=5;   
for(i=1;i<=num;i++){    
fact=fact*i;    
  }    
document.writeln("Factorial: "+fact); 
</script>

Example 3 in Python

fact=1
num=5;
fori in range(1,num+1): 
fact=fact*i

print("Factorial:  "+str(fact))

Example 3 in Ruby

fact=1
num=5
fori in 1..num do 
fact=fact*i
end
puts "Factorial: #{fact}"

Example 3 in PHP

<?php
$fact=1;
$num=5;
for($i=1;$i<=$num;$i++){  
  $fact=$fact*$i;
}  
echo "Factorial: $fact";  
?>

Example 3 in Swift

var fact=1;
varnum=5;
fori in 1...num {
fact = fact * i;
}
print("Factorial: ",fact)

Example 3 in Rust

fn main() {
letmut fact=1;
letmutnum=5;
fori in 1..num+1 {
fact=fact*i;
}
println!("Factorial: {}", fact); 
}

Output:

Sum=1275

Example 4 in C

#include <stdio.h>
void main()
{
    int i, j, k, space=10;

    for (i=0;i<=5;i++)
    {
        for (k=0;k<space;k++)
        {
        printf(" ");
        }
        for (j=0;j<2*i-1;j++)
        {
        printf("*");
        }
        space--;
         printf("\n");
    }
}

Example 4 in C++

#include <iostream>
using namespace std;

int main()
{
    int i, j, k, space=10;

    for (i=0;i<=5;i++)
    {	
        for (k=0;k<space;k++)
        {
        cout<<" ";
        }
        for (j=0;j<2*i-1;j++)
        {
     cout<<"*";
        }
        space--;
         cout<<"\n";
    }
}

Example 4 in C#

using System;  
public class ForExample  
    {  
      public static void Main(string[] args)  
      {  
    int i, j, k, space=10;

    for (i=0;i<=5;i++)
    {	
        for (k=0;k<space;k++)
        {
        Console.Write(" ");
        }
        for (j=0;j<2*i-1;j++)
        {
         Console.Write("*");
        }
        space--;
         Console.WriteLine(" ");
    }
}}

Example 4 in Java

public class ForExample{

     public static void main(String []args){
            int i, j, k, space=10;
    for (i=0;i<=5;i++)
    {	
        for (k=0;k<space;k++)
        {	
       System.out.print(" ");
        }
        for (j=0;j<2*i-1;j++)
        {
        System.out.print("*");
        }
        space--;
        System.out.println("");
    }
     }
}

Example 4 in JavaScript

var space=10; 
for (i=0;i<=5;i++)
    {	
        for (k=0;k<space;k++)
        {	
document.writeln("\xa0");
        }
        for (j=0;j<2*i-1;j++)
        {
    document.writeln("*");
        }
        space=space-1;
      document.writeln("<br>");
    }

Example 4 in Python

space=10
for i in range(0,6):	
    for k in range(0,space):
        print(" "),
    for j in range(0,2*i-1):
        print("*"),
    space=space-1
    print("")

Example 4 in Ruby

space=10
for i in range(0,6):	
    for k in range(0,space):
        print(" "),
    for j in range(0,2*i-1):
        print("*"),
    space=space-1
    print("")

Example 4 in PHP

<?php  
$space=10;
for($i=0;$i<=5;$i++){  
   for ($k=0;$k<$space;$k++)
        {
      echo " ";
        }
  for ($j=0;$j<2*$i-1;$j++)
        {
       echo "*";
        }
  $space--;
  echo "\n";
}  
?>

Example 4 in Swift

var space=10;
for i in 0...4 {
 for k in 0...space
 {
     print(" ", terminator : "")
}
 for j in 0...2*i
 {
     print("*", terminator : "")
 }
 space=space-1;
 print("")
}

Example 4 in Rust

fn main() {
  let mut space=10;  

     for i in 0..5 {

    for k in 0..space+1 {
          print!(" ");

     }
     for j in 0..2*i+1 {
          print!("*");
     }
     space=space-1;
     println!("");
}
}

Output:

*
***
         *****
        *******
       *********
      ***********

Infinite Loop

Let's see the simple program of usage of an infinite loop in respective languages:

Program in C

#include <stdio.h>
#include<conio.h>
int main()
{
  char ch=' ';
   do{
   printf("javaTpoint");
  ch=getch();
  if(ch=='y')
  break;
   }while(true);
    return 0;
}

This program creates an infinite loop. Until and unless, we press the key y, this loop continues. When we press the key 'y', this leads to the termination from the loop.

Program in C++

#include <iostream>
using namespace std;
int main()
{
  
 char ch=' ';
   	
   do{
   
        cout<<"javaTpoint";
       ch=getchar();
 
   }while(ch!='y');
    return 0;
}

This program creates an infinite loop. Until and unless, we press the key 'y', this loop continues. When we press the key 'y', this leads the termination from the loop.

Program in C#

using System;

namespace Project
{
    class MainClass
    {
        public static void Main (string[] args)
        {
            bool key = false;
            do
            {
                Console.Write ("JavaTpoint");
                
            }while(Console.ReadKey().Key!=ConsoleKey.Enter);
        }
    }}

This program creates an infinite loop. Until and unless, we press the key ?Enter?, this loop continues. When we press the key enter, it leads to the termination from the loop.