Loops in C!!
Tags: firstpost, computerscience, programming, codenewbie
Published: 2021-01-02 08:10:52



**Loops are really useful in programming**
they reduce lines of code and make our work easy.
Now suppose we have to print Hello World  five times then without loop we have to write 5 printing statement something like this



 ```int main() {
   printf( "Hello, World!\n");
   printf( "Hello, World!\n");
   printf( "Hello, World!\n");
   printf( "Hello, World!\n");
   printf( "Hello, World!\n");
}``` 

But with the help of Loop, we can do it in a simpler way



 ```int main() {
   int i = 0;
   while ( i < 5 ) {
      printf( "Hello, World!\n");
      i = i + 1;
   }
}```
so both the codes gave the same output i.e.
Hello, World!
Hello, World!
Hello, World!
Hello, World!
Hello, World!

*Now imagine printing Hello, World! hundred times😶
Then definitely first code is not a sensible one so we go for the second one i.e loops*



So here we have 2 types of loops-

**Entry Controlled.**

![Alt Text](https://dev-to-uploads.s3.amazonaws.com/i/qvfbd5lmztju80pm2wsr.PNG)
    Entry controlled loop is like a door which has condition set to be fullfiled as seen in the picture i.e firstly we satisfy the condition then the door opens.

**Definition**
An entry control loop checks the condition at the time of entry and if condition or expression is true then control transfers into the body of the loop.
Such type of loop controls entry to the loop that’s why it is called entry control loop.

For Example- for,while

**Exit-controlled.**
![Alt Text](https://dev-to-uploads.s3.amazonaws.com/i/2no9it2npn1ool2noufl.PNG)
So now in this picture you can see the door is opened and the person get inside and then he is checked
so he gets a chance to enter the room  atleast once even if he does not satisfy the condition set of entering.

**Definition**
Exit controlled loop is a loop in which the loop body is executed first and then the given condition is checked afterward. In exit controlled loop, if the test condition is false, loop body will be executed at least once.  
For Example- Do While Loop.


So let's dive into the syntax of these loops

**for loop**

**Syntax**
```for (initializationStatement; testExpression; updateStatement)
{
    // statements inside the body of loop
}```


**while loop**

**Syntax**
```while (testExpression) 
{
    // statements inside the body of the loop 
}```


**do-while loop**

**Syntax**
```do {
   statement(s);
} while( condition );```

 **Infinite loops**

 So infinite loop is one which has no condition to be fullfiled or to terminate the loop so loop keeps on running.
    like in this case the loop will continue printing Hello World infinite times
  **Infinite for loop**  
```int main()  
{  
   for(;;)  
   {  
     printf("Hello World"); // loop runs infinitely
   }  
return 0;  
}``` 


**Infinite while loop** 

```while(1) or while(any non-zero integer)
{ 
     printf("Hello World");
}```

Infinite loops become useful when we are making Menu driven program in which we want menu to be displayed again and again unless user exits.
Used when you need to do some calculation before you know the exit condition.

**Empty loop**
Loop without body.
You can use it to delay execution of next operation for some time.
```for(i=1 ; i<10 ; i++)```
```{
   }```