#include <stdio.h>
main(){
FILE *out_file;
int i, n;
  printf("Input n ");
  scanf("%d",&n);
  out_file=fopen("ff.c","w"); 
  fprintf(out_file, "%s","main(){");
  fprintf(out_file, "\n");
  fprintf(out_file, "%s","int ");
  fprintf(out_file, "\n");
  for (i=1;i<=n;i++) {
    fprintf(out_file, "%s","a");
    fprintf(out_file, "%d ",i);
    if (i<n)
    fprintf(out_file, "%s",",");
    else
    fprintf(out_file, "%s",";");
  };
    fprintf(out_file, "\n");
  for (i=1;i<=n;i++) {
    fprintf(out_file, "%s","a");
    fprintf(out_file, "%d ",i);
    fprintf(out_file, "%s","=");
    fprintf(out_file, "%d",i);
    fprintf(out_file, "%s",";");
    fprintf(out_file, "\n");
  };
  fprintf(out_file, "%s ","}");
}

Generated program
main(){
int 
a1 ,a2 ,a3 ,a4 ,a5 ,a6 ,a7 ,a8 ,a9 ,a10 ;
a1 =1;
a2 =2;
a3 =3;
a4 =4;
a5 =5;
a6 =6;
a7 =7;
a8 =8;
a9 =9;
a10 =10;
}