What is the difference between #define n 100 and int n=100 ?

[fatma1000]

help2 in c++

what is the difference between

#define N 100
double H[N];

and
int N=100;
double H[N];

 

[saeid5977]

help2 in c++

hi
secound code does not works
cuz when u declear an static array compiler should knows the dimention of that and in this condition the value of N is unknown in compile time until run time.

but in first code u use from precompiler expresion #define that is same as u write int H[100];

if u want to create an array with dynamic dimention use from new and delete operations.


int *H=NULL;
int N=100;
H=(int*) new int[N];
.
.
.
use from H like an array and when u dont need it any more. u should free memory of it:

delete[] H;
H=NULL;

 

[sshahid47]

help2 in c++

Hi,

int N=100;
double H[N];

this will not work, however

const int N=100;
double H[N];

this will work and the difference between

1)
#define N 100
double H[N];

and

2)
const int N=100;
double H[N];

in case 1, the compiler simply replace the N with the number defined and compiles the code, this is done during the precompilation phase of the compiler

in case 2, the compiler compiles the code as it is and i would recommend this because the code is more type safe this way.