What is (<some command/variable> i = 0; i < z; i++)?

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1

I’ve seen 3 different programming languages with that exact same coding structure, what does it mean? What is i, and what is i++?

2

It’s a C-style for loop, typical full syntax is

for (initialization; condition; post) { /* loop body */ }

Your example would be something like

for (int i = 0; i < z; i++) { /* ... */ }

i in this case would be an integer.
i++ means “increment i by 1”.

Semantically it’s like this:

  1. Assign 0 to i.
  2. Check if i is less tnan z.
  3. If it isn’t, go to (7).
  4. Execute loop body (in which current value of i is available).
  5. Increment i by 1.
  6. Go to (2).
  7. End.

More information e.g. here.

3

Okay, I could see that, so int means initial value or integer?

4

Integer.

5

int is a type declaration. It declares that the variable i contains an integer.

Furthermore, it declares that the variable referred-to as i within the body of this loop exists only within the body of this loop! (This helps to prevent unwanted interference between loops, so-called “coupling” caused by using the same variable in more than one place.)

  1. First, i is initialized to zero. Then, the loop begins.
  2. The loop executes zero or more times, while (i < z). (If the condition is initially false, the loop does not execute at all.)
  3. At the end of each execution of the loop, i is incremented (i++).

This construct first appeared in the now-venerable C programming language, circa 1971, and has been shamelessly copied ever since. (I don’t know if they cabbaged it from something even older …)

6

footnote, even though you usually see

type declaration = value;
if (value < maximum)
{
    value++;
}

that’s the same as

type declaration = value; if (value < maximum) { value++; }

you’re only filling in data for a structure of sorts, the kind of that a compiler would know about. <command> arg arg arg — or — <command>(arg; arg; arg), the first one is more of a console thing and then programs do language the other way, most of the time at least. Brainfuck is a thing you guys. Think about that.

7

Something about that doesn’t make sense. I’ve definitely 100% used the variable “i” after defining it as a loop in other places outside the brackets, and it worked exactly as expected as a parameter I could arbitrarily float.

8

“Winging it” is a really, really bad idea. Just saying.

1 Like
9

That’s… not how scope works

2 Likes
10

I stand by what I said:

https://www.quora.com/How-can-I-declare-multiple-variables-in-C-inside-a-loop-so-that-at-any-iteration-a-new-variable-is-declared?share=1

However, you should not declare the variable ambiguously, such that there might be simultaneously more than one interpretation of i. I believe that the compiler should actually call-you-out on that. Do not declare i at the function or global level if you at the same time use the same identifier within a loop or block context.