Les fichiers en Langage C! aidez-moi!!

#include<stdio.h>
#include<malloc.h>
#include<conio.h>
#include<string.h>
int N;
int * In (char nom[30])
{
        printf("donner le fichier source : \n");
         gets(nom);
        FILE *a;
        int i=0;
        a=fopen("a.txt","r");
        if(a==NULL) { printf ("erreur");
                      getch ();
                      exit (0);
                      }


        fscanf(a,"%d\n",&N);
        int *t= (int*) malloc (sizeof(int)*N);
        while(!feof(a)) {
              fscanf(a,"%d\n",&t[i]);
              //printf("T[%d] = %d\n",i,t[i]);
              i++;
        }
        fclose(a);
        return t;
}
void Out(char nom[30],int *t){
     printf("donner le fichier destination : \n");
     gets(nom);
     FILE *f;
     strcat(nom,".txt");
     f=fopen(nom,"w");
     fprintf(f,"%d\n",N);
     int i;
     for(i=0;i<N;i++)
        fprintf(f,"%d\n",t[i]);
     fclose(f);
}
int * permutation(int *t){
      int i,j,x;
      for(i=0;i<N-1;i++)
      {
         for(j=i+1;j<N;j++){
              if(t[j]>t[i]){
                  x=t[j];
                  t[j]=t[i];
                  t[i]=x;
              }
         }
      }

      return t;
}

void Print(int *T){
     int i;
     for(i=0;i<N;i++)
             printf("T[%d] = %d\n",i,T[i]);
}

void Tri(char nom[30],int *t){
    t=In(nom);
    Print(t);
    t=permutation(t);
    Print(t);
    Out(nom,t);
}
int main ()
{
      int *T;
      char nomf[30];


     /*T=In(nomf);
     Print(T);

     Out(nomf,T);*/
     Tri(nomf,T);
     getch ();
     return 0;
        }