Struct, linked list, head,null-pointer, C++ -

how can define,that pointer head shows first linked list element?the compiler shows mistake in place :

head=domino->info;

struct dominopart { int number1; int number2;    };  struct dominoone { dominopart info; struct dominoone *next; }; 

first defined null-pointer,because linked list empty @ first.

  struct dominoone* next= null;     struct dominoone* head=null; 

then information file read line line.

    int readdomino (){         file *datei;           if((datei=fopen("datei.dat", "r") )==null) {              std::cout<<"file can't opened"<<std::endl;             return 0;         }else {             int beginning;             int temp;             fscanf(datei, "%d", &beginning);              for(int i=0; i<beginning; i++) {                  dominoone *domino= new dominoone;                 fscanf(datei, "%i", &temp);                 domino->info.number1=temp;                 fscanf(datei, "%i", &temp);                 domino->info.number2=temp;                 printf("[%d:%d]", domino->info.number1, domino->info.number2);                 domino->next=0;                  if(i==1) {                     head=domino->info; //the compiler shows mistake here                 }             }          }return 0;      } 

the file read , shows this,that have written in file correctly,but can't delete whole list,because pointer head still null-pointer:

void del () {     dominoone* tmp;     while(head != 0) {          tmp=(head)->next;         delete head;         head=tmp;     }  } 

there few errors in code.

first assignment head=domino->info cannot performed since types of left , right sides incompatible.

second, on reading list of dominos, need keep track of tail of list.

so need declare

  struct dominoone* tail=null; 

then after have populated structure replace if (i==1) ... with

  if (i == 0 ) head = domino;   else tail->next = domino;   tail = domino; 

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the final version of readdomino() function might this:

int readdomino (){         file *datei;         struct dominoone* tail=null;           if((datei=fopen("datei.dat", "r") )==null) {             std::cout<<"file can't opened"<<std::endl;             return -1;         }          int list_size;         fscanf(datei, "%d", &list_size);          for(int i=0; i<list_size; i++) {                 dominoone *domino= new dominoone;                 fscanf(datei, "%i", &domino->info.number1);                 fscanf(datei, "%i", &domino->info.number2);                 printf("[%d:%d]\n",                        domino->info.number1,                         domino->info.number2);                 domino->next=null;                  if (i == 0 ) head = domino;                 else tail->next = domino;                 tail = domino;            }         }         return 0; }