Question

I’m encountering a problem trying to generalize my algorithm for any-size problems.
The code is working for the test problem I used, but I had to insert manually the lenght of some arrays. Next, I’ve tried reading the lenght of input files in two variables, but then I’m not able to use them in all of my code, but just in some pieces. I think it’s quite a stupid thing, but I’m really new to C++ and I’d like to get help.
Here’s the piece of code:

#include <fstream>
#include <iostream>
#include <time.h>



using namespace std;

struct node{
int     last_prod;
int     last_slot;
float   ZL;
float   ZU;
float   g;
bool fathomed;
node *next;
node *padre;
node *primofiglio;
};

clock_t start, end;
double cpu_time_used;


int l=0;
int cont_slot=0;
int cont_prod=0;
float temp_cont;

float   distanze[360];                                // dichiarazione variabili
int     slot[111];
int     slot_cum[111];
float   COIp[111];
int     domanda[111];
float   Zb=9999999999999999;                            
float   LowerBound(struct node *n);
float   UpperBound(struct node *n);
float   h(struct node *l,struct node *n);
void    creasottolivello(struct node *n);
void    fathRule2(struct node *n);
void    fathRule3(struct node *n);
void    stampaRisultati(struct node *n, ofstream &f);
int     unFathomedNodes(struct node *n);
void    append(struct node* temp, struct node* n);
void    ricercaOttimo(struct node *n, ofstream &f);
void    calcoloBounds(struct node *n);

int main(){

start = clock();

ifstream contdist_file ( "/Users/MarcoBi/Desktop/TESI di LAUREA/Xcode/dati/distanze.txt"     );  // conteggio dati input


if ( !contdist_file.is_open() ) {                   //conta righe file slot
}
else {
    for(int i=0; !contdist_file.eof(); i++){
        contdist_file >> temp_cont;
        cont_slot++;
    }
}

ifstream contslot_file ( "/Users/MarcoBi/Desktop/TESI di LAUREA/Xcode/dati/slot.txt" );

if ( !contslot_file.is_open() ) {                  //conta righe file prodotti
}
else {
    for(int i=0; !contslot_file.eof(); i++){
        contslot_file >> temp_cont;
        cont_prod++;
    }
}
....

As you can see, in the main() I count the lenght of input files into cont_prod and cont_slot variables, but then I can’t use them in variable declaration. The variable lenght arrays I need have to be global variables ‘cuz I need them also in other functions. And also cont_prod and cont_slot need to be global, as I need them in local variable declarations in some functions.
Here is one of the functions I need to use them in:

float LowerBound(struct node *n){                //funzione LowerBound
int S[111];
int Sp=0;
float d[111];
float dmin[111];
float D;
float LB;

for(int i=n->last_prod;i<111;i++){
    Sp=Sp+slot[i];
}
for(int i=0;i<111;i++){                     //Calcolo S_pigreco
    S[i]=0;
}

if(n->last_prod==0){                         //condizione necessaria per nodo radice
    S[0]=slot[0];    
    for(int i=n->last_prod +2;i<111;i++){
        for(int j=n->last_prod +1;j<=i;j++){
            S[j]=S[j-1]+slot[j];
        }
    }
}
else{
    for(int i=n->last_prod +1;i<111;i++){
        for(int j=n->last_prod;j<=i;j++){
            S[j]=S[j-1]+slot[j];

        }
    }  
}
S[110]=S[109] + slot[110];

//calcolo somma distanze da slot j+1 a q
for(int i=0;i<111;i++){
    d[i]=0;
}

for(int j=n->last_prod;j<111;j++){
    for(int i=n->last_slot; i < n->last_slot +S[j]; i++){
        d[j]=d[j]+distanze[i];
    }
}

//calcolo dmin_pigreco
for(int i=n->last_prod; i<111; i++){
    dmin[i]= d[i]/S[i];
}

D=0;
for(int i=n->last_prod; i<111; i++){
    D=D+dmin[i]*domanda[i];
}
LB=n->g+2*D;                                           
return LB;                                 
}

111 is cont_prod and 360 is cont_slot.
I’m programming on a Mac in Xcode and it says that variable lenght arrays cannot be declared at file scope, which I think it means as global variables.
How can I manage that?

Answer 1

Perhaps declare pointers at file scope and allocate memory dynamically as and when you know the values…

Declare

   int     *slot

and allocate memory as

slot = new int[cont_slot];

and after using dont forget to “delete [] slot” it .. 🙂