C Programming - Control Instructions - Discussion

To execute a group of statement repeatedly we use Loops(may be any kinds of loop).C provides three types of Loop(for, while, do..while) for use in difference places according to situation, that means all things that can be done using a for loop can also be done using a while loop. If you failed give the Question in my mail (basanta.mca[at]gmail.com) I will solve it.

For loop is ultimately broken down to same machine code as a while loop doing same function. So their speed might be same.

Why statement 4 is true ?

@Deepa

The following is the valid for loop.

int i=0;

for(;;)
{
printf("%d ", i++);

if(i == 10) break; // condition checking is done here.
}

"for loop can be used if we want statements in a loop get executed at least once. ".

How? Can you tell that the above statement is write please explain.

@Thiyagarajan

Yes. The 'for-loop' can be used if we want statements in a loop get executed at least once.


/* The following is the code that you have requested. */

/* ----- Usually we write code with do-while loop ----- */

int num = 0;

do
{
printf("Enter a number : ");
scanf("%d", &num);

}while(num != 0);


/* ----- Same logic with for loop ----- */

int num = 0;

for(;;)
{
printf("Enter a number : ");
scanf("%d", &num);

if(num == 0) break;
}

I hope this will help you. Have a nice day!

for loop is not end with semicolon (;)

for(i=0;i<n;i++)
{

}

Then why statement 3 is correct ?

@Srinivas

See its not compulsary that for loop should have body for execution...so we can write for(i=0;i<n;i++); i.e for without body... but as here our for is 'for(;;)' it go infinite
so statement three is correct..

I hope you understood what i mean to say...

Here I can say that 4th statement is wrong, because it is not sure that a for loop can atleast be executed one time.

Have a look at the following :

int main()
{
int i;
for(i=0;i>5;i++) //at first time only condition fails
printf("hi");
}

For 4th statement do_while loop only correct.