what does this error mean?

[viral ivy]

trying to make a 10 digit random prime number generator:heres the full code,do criticise it im a very begginer

[real shell]

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@viral ivy

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[viral ivy]

#include <cstdlib>
#include <ctime>
#include <iostream>
int nfunc(int){
 srand(time(0));
    return rand() % 999999999;

}
bool primvar(int n) {

  for (int i = 2; i <= n / 2; --i) {
    if (n % i == 0) {
      std::cout << "not prime";
      return true;
    } 
  }return false;
}
int main() {
  int primerand; 
  for(bool c=true;!c;){ 
  if (primvar(nfunc(int))){
    primerand=(nfunc(int));
    c=false;
               }}
  std::cout << primerand ;
  return 0;
}```

[tame turtle]

You're putting types where the function parameter should be

And ofc, doing srand(0) every call makes it not random

Srand(0) should be called once per program

[viral ivy]

oh right,that should be in main

[reef kraken]

it's srand(time(0))

[tame turtle]

Yeah

Mb

[reef kraken]

you just have to wait a second for it to be random

[tame turtle]

No?

Ah

Yeah

[viral ivy]

so what do i put in the function?

[tame turtle]

Idk

U dont even use the parameter

No idea why u put it there

[viral ivy]

but if its a void function it wont return anything?

[reef kraken]

for(bool c=true;!c;) think about this loop for a second

[tame turtle]

You put parameter

The (int)

Not return

[viral ivy]

i mean when calling the function

[tame turtle]

I meant both

[viral ivy]

the sili

[viral ivy]

but the function doesnt need a parameter

[tame turtle]

But in signature you put (int)

In the function declaration

[viral ivy]

well yes so it isnt void and returns int?

[tame turtle]

Bruh

int func(int)

The (int)

Not int but (int)

The thing in ()

[viral ivy]

i have misunderstood

lemme try something

ah wait,when calling the func with srand in main,will rand in the func still use srand? @tame turtle

[tame turtle]

When you call a function it executes code inside

Srand is a global function

Only one

[viral ivy]

its the same if it was for(bool c=false;c;) right?

[tame turtle]

And affects every rand()

[viral ivy]

i see

[reef kraken]

yep

[tame turtle]

Just make a normal variable and sane loop condition

This is unreadable

[viral ivy]

im gonna use this code to practise reverse engineering and check if that conditon affects the assembly as well

its unreadable on purpose

[tame turtle]

It doesnt affect assembly much

[viral ivy]

worth the try

the pseudocode as well

[viral ivy]

the output comes as 0

everytime

[tame turtle]

Yeah

Compiler optimizes it

[viral ivy]

?

[tame turtle]

;asm -O2

int main(){
if(char var = 0){
    var = 4;
}
}

[hollow token]

Assembly Output

main:
  xor eax, eax
  ret

.makian | 84ms | c++ | x86-64 gcc 14.2 | godbolt.org

[viral ivy]

this bot is very cool

[tame turtle]

As you see

Optimized away

No if exists

[viral ivy]

shoudnt that be int var =4

[viral ivy]

why?doesnt that break the program

[tame turtle]

Nope

Because the condition is always 0

[tame turtle]

Var is already declared in if

[tame turtle]

The if wont ever execute

Only if you have else but then it'll still be as if the if doesnt exist

[viral ivy]

but the if will eventually?

how would the compiler know that

[tame turtle]

because its smart

Compilers do crazy optimizations

Anything goes as long as the program runs expectedly

[viral ivy]

;asm -O2

int main(){
int var =0;
if(var == 0){
    var = 4;
}
}```

[hollow token]

Assembly Output

main:
  xor eax, eax
  ret

heisenbergs_revengance | 53ms | c++ | x86-64 gcc 14.2 | godbolt.org

[viral ivy]

ah

but the if statement does execute here?

[tame turtle]

Where exactly

[viral ivy]

var is equal to 0

[reef kraken]

the program works as if it were executed in the way you expect

that is sufficient

[tame turtle]

Eax is the function return value

If you want to know RE, learn asm

[viral ivy]

got it

[viral ivy]

so var wont equal to 4 there?

[devout sandal]

It doesn't because you don't use it

Try printing it out

To your terminal

It will still look different on asm

But just see

[tame turtle]

;asm -O2

#include <iostream>
int main(){
int var =0;
if(var == 0){
    var = 4;
}
std::cout << var;
}```

[hollow token]

Assembly Output

main:
  sub rsp, 8
  mov esi, 4
  mov edi, OFFSET FLAT:std::cout
  call std::basic_ostream<char, std::char_traits<char> >::operator<<(int)
  xor eax, eax
  add rsp, 8
  ret

.makian | 651ms | c++ | x86-64 gcc 14.2 | godbolt.org

[tame turtle]

Already optimizes it and just sets it to 4

Doesnt even set it

Just gives the 4 as param

[viral ivy]

cool,but in my program i do print it out

[tame turtle]

I mean ^^

[viral ivy]

alright holdon

[devout sandal]

You could do something like
X = 10 * 5 + 10/2 or whatever and you will still get this

[tame turtle]

Yup

Since nothing is done

So compiler just says meh, it does nothing so lets scrap it all

[devout sandal]

If you try printing it it will also not calculate them as the compiler can pre calculate it and write a value to give

The actual behavior stays the same either way

Your program behaves as if it did do whatever step you wrote in your code

On anything above O0 ofc

[tame turtle]

Except one pesky

(-Ofast)

[devout sandal]

Gamer move

[tame turtle]

But yeah, as long as behavior remains the same, compiler can do whatever it wants

[viral ivy]

alright

int main() {                                     
  srand(time(0));                   
  int primerand;                                 
  for (bool c = true; !c;) {                     
    if (primvar(nfunc())) {                   
      primerand = (nfunc());                     
      c = false;                                 
    }                                            
    std::cout << c<<":bool is";                 
  }                                              
  std::cout << primerand << ": prime is" << std::
  return 0;                                      
}                                                

the bool is is probably unnecasarry

[viral ivy]

but it still prints 0,even after doing the same here

[devout sandal]

You mean this prints 0?

[viral ivy]

yes

and bool is doesnt orint

p*

[devout sandal]

Yeah because your for loop never executes

Also not initializing variables

int primerand = 0;
Or primerand {} much preferred

[viral ivy]

why?

[devout sandal]

Try to think of what your for loop condition does

C = true

And loop will only execute while c is not true

!c means c is not true

It's the same thing as
If c != true
continue loop

[viral ivy]

got the bool to print,
is

    if (primvar(randomNumber)) { /```
different than 
``` if (primvar(nfunc())) {```?

[devout sandal]

Different in what way

[viral ivy]

do they do different things?not in the more redable way?

[devout sandal]

The primevar function might do something different, return different stuff but an if statement only does one thing
If(condition met)
Execute

[viral ivy]

wait,so is

      primerand = (nfunc());
      c = true;```
different from
```int randomNumber = nfunc(); 
    if (primvar(randomNumber)) { 
        primerand = randomNumber; ```

ah it is

well i got it to technically work

its just that it keeps printing 3/other singler digit prime nums

and it takes like 2 whole seconds

[viral ivy]

got it to work,thanks guys

i appreaciate that this server only hints at the answer most of the time

!solved