//Pgm-2: Go-Back-N ARQ & Selective Repeat ARQ Sliding Window Protocol
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<unistd.h>
int n,r;
struct frame
{
char ack;
int data;
}frm[10];
int sender(void);
void recvack(void);
void resend(void);
void resend1(void);
void goback(void);
void selective(void);
int main()
{
int c;
do
{
printf("\n\n1.Selective repeat ARQ\n2.Goback ARQ\n3.exit");
printf("\nEnter your choice:");
scanf("%d",&c);
switch(c)
{
case 1:selective();
break;
case 2:goback();
break;
case 3:exit(0);
break;
}
}while(c>=4);
}
void goback()
{
sender();
recvack();
resend1();
printf("\n all packets sent successfully\n");
}
void selective()
{
sender();
recvack();
resend();
printf("\nAll packets sent successfully");
}
int sender()
{
int i;
printf("\nEnter the no. of packets to be sent:");
scanf("%d",&n);
for(i=1;i<=n;i++)
{
printf("\nEnter data for packets[%d]",i);
scanf("%d",&frm[i].data);
frm[i].ack='y';
}
return 0;
}
void recvack()
{
int i;
rand();
r=rand()%n;
frm[r].ack='n';
for(i=1;i<=n;i++)
{
if(frm[i].ack=='n')
printf("\nThe packet number %d is not received\n",r);
}
}
void resend() //SELECTIVE REPEAT
{
printf("\nresending packet %d",r);
sleep(2);
frm[r].ack='y';
printf("\nThe received packet is %d",frm[r].data);
}
void resend1() //GO BACK N
{
int i;
printf("\n resending from packet %d",r);
for(i=r;i<=n;i++)
{
sleep(2);
frm[i].ack='y';
printf("\nReceived data of packet %d is %d",i,frm[i].data);
}
}

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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
}