While or for loop?

Hi, I want to write a script which will evaluate the lowest factorial which is greater than the user's input, and I am unsure of whether to use a while or a for loop to execute this. Any help is always much appreciated! This is my code so far:

num=input('Enter a number: ');

n=0;
while (true)
    n=n+1;
    f(1i)=factorial(n);
    if f(1i)>num
        formatSpec='The factorial greater than %d is %d';
        fprintf(formatSpec,num,f);
    else
        continue
    end
end

[Guillaume]

Typically, you'd use a while loop if you don't know in advance how many times you're going to loop, and a for loop if you do. Therefore in your case, a while loop would be more appropriate.

However, note that you can always convert one to the other.

Answer 1

[Mehmed Saad]

1. Use while loop
2. instead of using if else and continue break in while(true), add condition in while loop
3. Print after the while loop ends

PS: you need a break condition for a while(true) type loop otherwise it will continue runing forever

[Mark Coughlin]

Thank you for your response Mehmed, is this correct?

num=input('Enter a number: ');

n=0;
while (true)
    n=n+1;
    f(1i)=factorial(n);
    if f(1i)>num
        break
    else
        continue
    end
end
formatSpec='The factorial greater than %d is %d';
fprintf(formatSpec,num,f);

[Mehmed Saad]

Type 1i in command window

1i
ans =

   0.0000 + 1.0000i

if you want to index f pass n to it and not 1i

f(n) and not f(1i)

Also now try to remove continue break and if else from the code and insert condition in

   while(condition_at_which_loop_should_break)

[Mark Coughlin]

Mehmed, I appreciate you taking the time to help me with this. Is this correct now?

num=input('Enter a number: ');

n=0;
while (f(n)>num)
    n=n+1;
    f(n)=factorial(n);
    break
end
formatSpec='The factorial greater than %d is %d';
fprintf(formatSpec,num,f);

[Rik]

If you set a break point in your code you can step through your code step by step. Also, running this code is a faster test to see if it works than posting it and waiting for a reply.

Think about your code structure. That loop will continue while some condition is true, hence the name. Why did you need break previously? (hint: true will always be true, but f(n)>num might not)

[Mehmed Saad]

1. break is not required
2. intialize f before while loop (is it necessary to index f, if not replace f(n) with f in your complete code)
3. While loop will check the condition before executing, so it will check f(n)>num when f is not defined error will occur. Now suppose f exist and you defined it as 1, then it will check f(n)>num now n is zero. But there are no such index as zero in MATLAB so error will occur. we define n = 1 so that while loop can check the condition.
4. while loop will break when the condition is false, and continue runing if condition is true. our condition is f(n)>num and f(n) = 1 and suppose num is 10. Now 1>10, answer is false. while loop will not run because the condition is false. What if we reverse the condition f(n)<=num i.e. while loop will keep runing untill f(n) is less than equal to num. when f(n) is greater than num while loop will break automatically
5. You have to print the last value of f and not the entire f values as f is an array so either put f(end) or f(n) in fprintf

[Mark Coughlin]

Thankyou very much Mehmed, your explanation was extremely informative and helpful. I realise the solution is a lot simplier than I initally thought. I got the code working.

num=input('Enter a number: ');

n=1;
while (f<=num)
    n=n+1;
    f=factorial(n);
end

formatSpec='The factorial greater than %d is %d';
fprintf(formatSpec,num,f); 

[Mehmed Saad]

Cheers.

Also when you ve problem in code apply break point approach first to detect problem as told by Rik.