Swap Nodes in Pairs

 1struct ListNode* swapPairs(struct ListNode* head) {
 2    if (head == NULL || head->next == NULL){
 3        return head;
 4    }
 5    struct ListNode * temp = head;
 6    int num_to_swap;
 7    while(temp != NULL){
 8        if(temp->next == NULL){
 9            break;
10        }
11        num_to_swap = temp->val;
12        temp->val = temp->next->val;
13        temp->next->val = num_to_swap;
14        temp = temp->next->next;
15    }
16    return head;
17}