string - Exam exercise about lists and pointers C -

i need fix exam exercise since teacher ask me how fix tomorrow @ oral test:

nodo *cancellatutto(nodo *a, char *k) {  nodo *p,*q;  p = a;  if (p == null)     return null;  while (p != null) {      if (strcmp(p->chiave, k) == 0 ) {           if (p->prec == null && p->succ == null)             return null;          if (p->succ == null && p->prec != null) {             q = p;              p = p->prec;             p->succ = null;             free(q);         }          if (p->prec == null && p->succ != null) {             q = p;              p = p->succ;             p->prec = null;             free(q);         }          if (p->prec != null && p->succ != null) {             q = p;              p = p->succ;             q->prec->succ = p;             p->prec = q->prec;             free(q);         }      } else { p = p->succ; }  }  return a; } 

this function should see if 2 string equals (one in struct linked list , other k string) , erase string equal k, there 2 output cases wrong:

case 1:

k : dog

if insert 3 strings in : dog -> cat -> cat function doesnt erase "dog" , show me output: dog -> cat -> cat (correct output cat -> cat)

case 2:

another error found is: if list : dog -> dog -> cat output dog -> dog -> cat (right output should be: cat)

all other cases should work right.

struct :

struct nodo { char *chiave; struct nodo *prec; struct nodo *succ; }; typedef struct nodo nodo; 

rest of code is: (read comprehend part personal test; useless exam)

int main() { nodo *lista=createliststring(); // create list visualizza(lista); // views char *stringa="ciao"; // create k string lista=cancellatutto(lista,stringa); // call function visualizza(lista); // views } 

please note need fix this, not write code.

please dont @ overflows, errors, , such things in these function! fix first function! others personal test.

@bluepixy has given really strong hint in comments, going expand on:

case 1:

k : dog

if insert 3 strings in : dog -> cat -> cat function doesnt erase "dog" , show me output: dog -> cat -> cat (correct output cat -> cat)

case 2:

another error found is: if list : dog -> dog -> cat output dog -> dog -> cat (right output should be: cat)

in both of these cases, string want remove occurs @ head of list. cancellatutto needs return new head of list in case, not a¹

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^{1. if a supposed represent head of list, please use more meaningful name variable, such head or listhead (or whatever native language equivalent be).}