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Insert in a linked list at the start

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• Insert in a linked list at start in Java
  • Here is a Java program that creates a list object and then insert it into a linked list at the start:

    class List // I want to use 1 prgram file for this example, so I put the List class here... { int value; List next; } public class insert { /* ========================================= insert(h, e): insert e at start of list h return new list A List variable is a reference variable !!! ========================================= */ public static List insert (List h, List e) { e.next = h; return e; // Return new list that starts at e } public static void main(String[] args) { List head = null; // Empty list List p; /* ------------------------------------------------- Create a list element and insert in List at head ------------------------------------------------- */ p = new List( ); p.value = 1; head = insert(head, p); // Insert p in head print(head); /* ------------------------------------------------- Create a list element and insert in List at head ------------------------------------------------- */ p = new List( ); p.value = 2; head = insert(head, p); // Insert p in head again print(head); } // Print the list public static void print(List h) { while (h != null) { System.out.printf("%d ", h.value); h = h.next; } System.out.printf("\n\n"); } }

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/C/Linked-list/insert.java

    How to run the program:

    To compile:   javac insert.java          To run: java insert

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• Insert in a linked list at start in C
  • You can literally translate the Java constructs into the C language constructs if you understand what each construct do !!!

    Here is the C program code for the above Java program:

    #include <stdio.h> #include <stdlib.h> struct List // This is the List class definition in C { int value; struct List *next; }; /* ========================================= insert(h, e): insert e at start of list h return new list The data type List is struct List * in C ========================================= */ struct List *insert (struct List *h, struct List *e) { e->next = h; return e; // Return new list that starts at e } void print(struct List *h); // We must declare print to avoid compile error void main(int argc, char *argv[]) { struct List *head = NULL; // Nul pointer NULL instead of null struct List *p; /* ------------------------------------------------- Create a list element and insert in List at head ------------------------------------------------- */ p = malloc( sizeof(struct List) ); p->value = 1; head = insert(head, p); // Insert p in head print(head); /* ------------------------------------------------- Create a list element and insert in List at head ------------------------------------------------- */ p = malloc( sizeof(struct List) ); // This is new List( ) p->value = 2; head = insert(head, p); // Insert p in head print(head); } // Print the list void print(struct List *h) { while (h != NULL) { printf("%d ", h->value); h = h->next; } printf("\n\n"); }

    It literally took me 2 minute to convert the Java code to C code....

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  • Example Program: (Demo above code)                                                
    • Prog file: /home/cs255001/demo/C/Listed-list/insert.c

    How to run the program:

    To compile:   gcc insert.c          To run: ./a.out

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  • Moral of this example:

    Understanding concepts in the most important determinant in learning to program in a different language All procedural languages use the same set of concepts The only difference in how to express the concept in the syntax of the programming language !!!