a little code explanation

[orhanli1]

i am new in c and these are my first codes.
I found a code in my pdf and i did't understand somethings about this code.
This is the code

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define UZUNLUK 10
int main()
{
    int i,sayilar [UZUNLUK];
    srand(time(NULL));
    for(i=0;i<UZUNLUK;i++)
    {
                          sayilar[i]=rand();
                          printf("sayi[%d]=%d\n",i,sayilar[i]);
                          system("pause");
    }
}

1) why we use #define ..... (can't we use int uzunluk=10);
2) i can't understand anything from srand(time... line

[ಠ_ಠ]

1) why we use #define ..... (can't we use int uzunluk=10);
2) i can't understand anything from srand(time... line

because UZUNLUK is a constant, it will not change anywhere within the program so it does not need to be a variable

without srand(time(NULL)) the program would generate the same random numbers each time it is run

[orhanli1]

thanks a lot.You help me so much

[vart]

because UZUNLUK is a constant, it will not change anywhere within the program so it does not need to be a variable

because in old c-standard (C89) you cannot use variable (even const var which will not change) as array size, only define

[orhanli1]

you are great friends thanks a lot