Newbie question about srand

I am new to C++ and still trying to understand the nuances of the the syntax. In the below example i am using the srand() function to set my random seed. I am just wondering why srand needs to be in the main part of my program and cannot be outside in the front end of the program?

thank you for your time

Code:

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int seed_storage = time( NULL ); //set seed_storage to random seed value
int randRange(int low, int high)
{
    return rand()%(high+1-low)+low; //take the modulus of the generated number with respect to the difference between the high and low values of the range then add low.
}
int hiddenNumber; //value to hold random generated number
int main()
{
srand(seed_storage); //use seed_storage value as seed for rand() function
while(true)
{
    hiddenNumber = randRange(0,100);
}
}

Originally Posted by Mathieas

I am just wondering why srand needs to be in the main part of my program and cannot be outside in the front end of the program?

Because it is a function call.

So function calls can only be present within the main function of the program, that makes sense. Thank you

Well, not quite. You can have function calls at file scope where they are used to initialise a global variable, but... why are you using global variables?

I am using global variables mostly because i am teaching myself and as a result I prob have bad habits(I am using the jumping into c++ online book). I was just reading global variables are not the way to go in most cases. I have used them for so long that i have become used to using them...

I am not sure i understood your 2nd response. Could you give an example?

Thank you again for your time, I still dont have a good sense on how to ask the proper questions and often times i lack the vocab needed to do a useful search.

One example would be if you changed line 10 to:

Code:

int hiddenNumber = randRange(1, 42);

Don't do that by the way, as it would get executed before the srand call and thus not end up random at all.

Edit: Actually your line 5 is already an example of that.

Originally Posted by iMalc

One example would be if you changed line 10 to:

Code:

int hiddenNumber = randRange(1, 42);

Don't do that by the way, as it would get executed before the srand call and thus not end up random at all.

Edit: Actually your line 5 is already an example of that.

Thank you for the reply. That makes sense however I am not quite clear why I call a function to int a variable but cannot call a function straight up, as in the srand case. What is the logic behind syntax?

thank you both for your time and expertise,

Jonathan

Originally Posted by Mathieas

That makes sense however I am not quite clear why I call a function to int a variable but cannot call a function straight up, as in the srand case. What is the logic behind syntax?

Well, if you just examine it at one level (at file scope), a program is a sequence of declarations. A function prototype is a declaration of that function; a function definition is also a declaration of that function. However, a function call is not a declaration of that function, hence you cannot place it at file scope. But within the syntax of the initialisation of a variable, it is okay, since that syntax is syntax to define the variable, and a definition of a variable is a declaration of that variable.

Originally Posted by laserlight

Well, if you just examine it at one level (at file scope), a program is a sequence of declarations. A function prototype is a declaration of that function; a function definition is also a declaration of that function. However, a function call is not a declaration of that function, hence you cannot place it at file scope. But within the syntax of the initialisation of a variable, it is okay, since that syntax is syntax to define the variable, and a definition of a variable is a declaration of that variable.

Laser,

Thank you, it is comming together slowly. So if i understand, function calls are allowed in the but not at the file scope level becuase that portion of the program is for declarations only. Another example to clairify, I could call a function within a function definition whether i am in the Main function or not becuase i am declareing that function is this correct?
Thank you again,

Jonathan

Originally Posted by Mathieas

Another example to clairify, I could call a function within a function definition whether i am in the Main function or not becuase i am declareing that function is this correct?

Yes. The body of a function definition is basically a compound statement, i.e., it contains a sequence of statements. Hence, a statement comprising of a function call is fine.