Looping

Loop is doing something multiple times.

Syntax:

for(  how many times )

{

//do something

}

it is pretty easy let's try to print hello world 10 times it should look like that:

for(10)

{

   printf("hello world");

}

Hmmm that's right but not in syntax to tell the computer do something multiple times you should make a counter.

what is a counter?
a variable that counts as much as you want.

The for loop : consists of 4 main parts "for(i=0;i<10;i++)"
make a variable as a counter like i in our example.

1. define your counter start "i=0"
2. define your counter end "i<10" which means don't exceed 9.
3. define your step "i++" which means let i increases by 1 each step.
4. the code that will be repeated.

so the code should look like this:

#include<stdio.h>

int main()

{

   int i;

   

   for(i=0;i<10;i++)      // as mentioned before no need for {} if it was only one line

             printf("Hello World\n");

  return 0;

}

output:

Hello World

Hello World

Hello World

Hello World

Hello World

Hello World

Hello World

Hello World

Hello World

Hello World

can i replace the start and end of the counter?
yes for sure you can put whatever end and whatever start to make it move 10 steps.
like i=1 and end will stop when i = 10 which mean that condition will be i<11.

but what is the sequence of implementing the for loop ?

for(1:  i=0;   2:  i<10  ;  4: i++)
   3:    printf("Hello World\n");

1. define counter start i=0    //done only once
2. check if counter exceed its limit or not i<10 //done 10 times
3. code to be repeated.
4. increment the counter by 1.   //done 10 times

Now try to write a program that print the numbers from 1 to 100.

#include<stdio.h>

int main()

{

   int i;

   

   for(i=1;i<101;i++)     

             printf("%d\n",i);

  return 0;

}

modify the previous program to ask the user to enter the end of the counter before counting.

#include<stdio.h>

int main()

{

   int i,end;

   

   printf("please enter a number\n");

   scanf("%d",&end);

   for(i=0;i<end+1;i++)     

             printf("%d\n",i);

  return 0;

}

why we made the condition i<end+1 ?

because the counter stop counting when the condition went false which means when i equals to end  that's means the last number won't be printed so we changed the end.

now modify the program to take the start and the end from the user

#include<stdio.h>

int main()

{

   int i,end,start;

   

   printf("please enter two number\n");

   scanf("%d%d",&start,&end);

   for(i=start;i<end+1;i++)     

             printf("%d\n",i);

  return 0;

}

Practice :

write a program that takes two number from user and print the odd numbers in between.

input:

1 10

output:

1 3 5 7 9

thanks so much :) salamo3alikom :)