Unexpected output while printing a linked list - c

Question

I got this code on codeblocks 13.12 in lubuntu 16.04
The program is running but the problem is that the first insertion is duplicated that is,
lets say i first insert integer "4" to the linked list. But i get the output as:
4 ,4 ,
#include <stdio.h>
#include <stdlib.h>
struct node {
int data;
struct node* next;
};
struct node* head = NULL;
void Insert(int c)
{
if(head == NULL) {
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
head = temp;
}
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
struct node* temp1 = head;
while (temp1->next != NULL) {
temp1 = temp1->next;
}
temp1 -> next = temp;
}
void print() {
struct node* temp = head;
printf("list is: \n");
while (temp != NULL) {
printf( "%d ,",temp->data);
temp = temp->next;
}
}
int main () {
printf("How Many Numbers?\n");
int a ,b ,c;
scanf("%d" , &b);
for(a = 0;a<b;a++) {
printf("Enter the numbers \n");
scanf("%d",&c);
Insert(c);
print();
}
return 0;
}

Answer 1

the problem is that the first insertion is duplicated
Reason:
You've mentioned if(head==NULL) correctly to check whether inserted node is first node or not but after this you did not mention else to restrict compiler.
So the compiler compiles both the if block and the code following it
So another node gets created after head with the same value c
that's the reason when you insert c=4, you get 4,4, as output
Solution
Try using your insert() with an else condition as
void Insert(int c)
{
if(head == NULL)
{
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
head = temp;
}
else
{
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
struct node* temp1 = head;
while (temp1->next!= NULL)
temp1 = temp1->next;
temp1 -> next = temp;
}
}
suggestion : you've mentioned this twice in you insert() function
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
just allocate temp once and then insert it at approprite position using if-else conditions. This reduces the number of lines of code too. do it this way:
void Insert(int c)
{
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
if(head == NULL)
{
head = temp;
}
else
{
struct node* temp1 = head;
while (temp1->next!= NULL)
temp1 = temp1->next;
temp1 -> next = temp;
}
}

Answer 2

That is because the Insert function "falls through" after initialising the first item, and inserts it again. Add return at the end of the code block.
void Insert(int c)
{
if(head == NULL) {
struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
head = temp;
return; //<-- add this line
}
...