invalid operands to binary expression ('ostream' (aka 'basic_ostream<char>') and 'void') - linked-list

Question

I have homework for Data Structure in college with LinkedLists ,
did the code but the compiler "eclips" shows me an error called
Description Resource Path Location Type
invalid operands to binary expression ('ostream' (aka 'basic_ostream') and 'void') LinkedLists.cpp /LinkedLists/src line 156 C/C++ Problem
and this is the code , so what's this issue ? and how can i fix it?
Thanks ^^
struct node {
int StudentNumber;
string name;
node *link,*data;
};
node *head,*newNode,*last;
string name;
int StudentNumber;
node* insert (){
char a='n';
cout<<"hello to linked lists insertion"<<endl;
cout<<endl<<"please write your name : ";
cin>>name;
cout<<"please put the student number : ";
cin>>StudentNumber;
head=NULL;
while(a!='n'||a!='N'){
newNode = new node ;
newNode->StudentNumber=StudentNumber;
newNode->name=name;
newNode->link=NULL;
if (head==NULL)
{
head=newNode;
last=newNode;
}else {
last->link=newNode;
last=newNode;
}//end else
cout<<"please write your name : ";
cin>>name;
cout<<endl<<"please put the student number : ";
cin>>StudentNumber;
cout<<"Do you want to insert new nodes ? y for yes , n for no ";
cin>>a;
}//end while
return head;
}//end insert function
// adding nodes function
void add() {
int j;
cout<<"please choose your option for adding new node : 1 for add at the beginning , 2 for add at the end ";
cin>>j;
if (head!=NULL)
{
switch (j)
{
// adding at the beginning
case 1 :
newNode=new node;
newNode->link=head;
head=newNode;
cout<<"please insert your node data : ";
cout<<"Student Name : "<<newNode->data<<endl<<"and student number is : "<<newNode->StudentNumber;
break;
// at the end
case 2:
newNode= head;
while (newNode->link!=NULL)
{
newNode = newNode->link;
}// end of while
last= newNode;
newNode = new node ;
newNode->link=NULL;
last->link=newNode;
cout<<"please insert your node data : ";
cout<<"Student Name : "<<newNode->data<<endl<<"and student number is : "<<newNode->StudentNumber;
break; // end of case adding at the end
}
}else {cout<<"The list is empty";}
}// ending of the adding nodes function
// delete node function
void deletion () {
int s;
cout<<"please choose your option for deleting nodes : 1 for delete the first , 2 for delete the last node ";
cin>>s;
switch (s) {
// delete the first node
case 1 :
newNode = head;
last=head->link;
head=last;
delete newNode;
break;
//delete the last node
case 2:
newNode=head;
last=head;
while (newNode->link!=NULL)
{
last=newNode;
newNode=newNode->link;
}
last->link=NULL;
delete newNode;
break;
}//end of the switch
}// end of delete nodes function
int main() {
int m;
cout<<"Welcome to LinkedLists Example"<<endl;
cout<<"enter your choice number , 1 for inserting nodes to the list , 2 for adding nodes , 3 for deleting nodes ";
cin>>m;
switch(m) {
case 1:
cout<<insert();
break;
case 2:
cout<<add();
break;
case 3:
cout<<deletion();
break;
}
return 0;
}

Answer 1

In your main function, you have these three lines:
cout<<insert();
cout<<add();
cout<<deletion();
If you look at the prototypes for these functions:
node* insert ()
void add()
void deletion()
Now we can see what the problem is. In the insert case, you are trying to pass a node* into cout. cout has no idea how to handle a node*. Similarly, add and deletion are passing a void into cout which cout doesn't know how to handle.
There are two solutions:
Pack a string inside of insert, add, and delete, then return that string to cout.
Remove cout from those lines.
I suggest the second solution. It's much simpler for your project, and it won't break whatever you plan to do with insert's return value. Your main function will look like this:
int main() {
int m;
cout<<"Welcome to LinkedLists Example"<<endl;
cout<<"enter your choice number , 1 for inserting nodes to the list , 2 for adding nodes , 3 for deleting nodes ";
cin>>m;
switch(m) {
case 1:
insert();
break;
case 2:
add();
break;
case 3:
deletion();
break;
}
return 0;
}