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iOS

Posted by Francis Chouquet
Francis Chouquet
290 Points

A bit lost with variables and functions

Hi there,

I just started the iOS Dev class, and so far so good (just finished the Scopes video). But there are few points that are a bit blurry for me. If someone could help me with simple words, that would be great.

  1. Variables

I learnt about int, float and char but I am still not sure when to use what. Could someone tell me simply when I should use one instead of the other ? Then, to display results, I just saw a %s, I know about %c and %d but is there somewhere a table that shows which one corresponds to the chosen variable ?

I understand mostly of these things but it is still a bit not clear for me :)

  1. functions

In the video about functions, Douglass uses the function "void" and I don't understand why he does use that function.

Thanks a lot for your help.

Francis

5 Answers

eirikvaa
eirikvaa
18,015 Points

Variables

When you want to use an int, a float or a char really depends on the application your developing. If you need to store a single character somewhere, use a char. Int vs float is all about precision: If you only need whole numbers (4,200,-30), then you go for an int, but if you need numbers like PI (3,14) or something with that kind of precision, then you use a float. It's really not much to it.

For format specifiers (%d and so on), you can check out this list. It's a little bit long and detailed, so I'll list the most commony used below:

  • int - %d
  • float - %f (there is also a double, but a float and a double is more or less the same)
  • char - %c
  • string - %s (a string is just a combination of characters)

Functions

Void is not actually a function, but what's called a return type. A function can either return something or not depending on what you specify. For example, the main function all C programs must have returns an integer: 

int main() {

  return 0;
}

Functions that don't return anything would have been written like this:

void function() {

}

See the difference? Functions don't have to return anything, that's why we use the void keyword.

Ask again if you have more questions.

Gunjeet Hattar
Gunjeet Hattar
14,483 Points
Gunjeet Hattar
Gunjeet Hattar
14,483 Points

Hi,

  • Variables
  • int represents an integer (numbers without a decimal (whole numbers if you may say) ). So when you need to use a number like selecting choices from 1-5 you wouldn't select a number like 2.5. So in situations like these you use int
  • You use float on the other hand to represent numbers with decimal points. For e.g. when calculating average marks of a class. A student could get 50.4 percent marks and using only integers (int) will not suffice
  • You use char to represent a character. Unlike String which is like a combination of characters, char can only represent one value . For e.g. if you want the users to select from a choice list A-G you cannot use integers so chars seem more appropriate

  • %s and %d are format specifiers . You use %s to represent string, %d to represent numbers . Technically if you have to output a string (like "Mark" which is not a number or a character) you use %s . More information here Apple Developer Link

  • Functions

  • void is just to specify that the particular function will not return any value. You could have a function like int some_function() .... this function will return an int value upon completion wheres when you don't want a function to return anything but just perform some action then you use void.

Hope that helps.

George S-T
George S-T
6,624 Points
George S-T
George S-T
6,624 Points

I would really recommend buying a notepad and making notes as you watch the videos, it really helps me and Im always looking back at them.

Francis Chouquet
Francis Chouquet
290 Points
Francis Chouquet
Francis Chouquet
290 Points

Hi guys,

Thanks for your answers. Now I see more clearly how it works. Not easy to find clear and simple explanations on the web. Yours are easy to understand. I can continue with a clearer vision now :)

Francis Chouquet
Francis Chouquet
290 Points
Francis Chouquet
Francis Chouquet
290 Points

That is what I am going to do. I was thinking about it yesterday. I keep all files on my computer and come back to them when I need them. But the last videos were a bit more though and I realized I need to take notes. Thanks George for the idea :)