/* This program swaps the nodes of linked list rather
than swapping the field from the nodes.*/

#include <stdio.h>
#include <stdlib.h>

/* A linked list node */
struct Node {
	int data;
	struct Node* next;
};

/* Function to swap nodes x and y in linked list by
changing links */
void swapNodes(struct Node** head_ref, int x, int y)
{
	// Nothing to do if x and y are same
	if (x == y)
		return;

	// Search for x (keep track of prevX and CurrX
	struct Node *prevX = NULL, *currX = *head_ref;
	while (currX && currX->data != x) {
		prevX = currX;
		currX = currX->next;
	}

	// Search for y (keep track of prevY and CurrY
	struct Node *prevY = NULL, *currY = *head_ref;
	while (currY && currY->data != y) {
		prevY = currY;
		currY = currY->next;
	}

	// If either x or y is not present, nothing to do
	if (currX == NULL || currY == NULL)
		return;

	// If x is not head of linked list
	if (prevX != NULL)
		prevX->next = currY;
	else // Else make y as new head
		*head_ref = currY;

	// If y is not head of linked list
	if (prevY != NULL)
		prevY->next = currX;
	else // Else make x as new head
		*head_ref = currX;

	// Swap next pointers
	struct Node* temp = currY->next;
	currY->next = currX->next;
	currX->next = temp;
}

/* Function to add a node at the beginning of List */
void push(struct Node** head_ref, int new_data)
{
	/* allocate node */
	struct Node* new_node
		= (struct Node*)malloc(sizeof(struct Node));

	/* put in the data */
	new_node->data = new_data;

	/* link the old list off the new node */
	new_node->next = (*head_ref);

	/* move the head to point to the new node */
	(*head_ref) = new_node;
}

/* Function to print nodes in a given linked list */
void printList(struct Node* node)
{
	while (node != NULL) {
		printf("%d ", node->data);
		node = node->next;
	}
}

/* Driver program to test above function */
int main()
{
	struct Node* start = NULL;

	/* The constructed linked list is:
	1->2->3->4->5->6->7 */
	push(&start, 7);
	push(&start, 6);
	push(&start, 5);
	push(&start, 4);
	push(&start, 3);
	push(&start, 2);
	push(&start, 1);

	printf("\n Linked list before calling swapNodes() ");
	printList(start);

	swapNodes(&start, 2, 5);

	printf("\n Linked list after calling swapNodes() ");
	printList(start);

	return 0;
}
by

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About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}