Optimal Program using C

#include< stdio.h>
#include< conio.h>
void main()
{
 int page[20],n,f,i,j,a[20],pf=0,k=0,match;
 clrscr();
 printf("enter the length of the reference string");
 scanf("%d",&n);
 printf("enter the frame size");
 scanf("%d",&f);

 printf("enter reference string");
 for(i=0;i< n;i++)
 scanf("%d",&page[i]);
 for(j=0;j< f;j++)
 a[j]=-1;

 printf("\n-1\t-1\t-1\n\n");

 k=0;
 for(i=0;i< n;i++)
 {
  match=0;
  for(j=0;j< f;j++)
  if(a[j]==page[i])
  {
   match=1;
  }
  if(match==1)
  {
   goto x;
  }

  for(j=0;j< f;j++)
  if(a[j]==-1)
  {
   a[j]=page[i];
   pf++;
   goto x;
  }

  a[k]=page[i];
  k=(k+1)%f;
  pf++;
  x:;
  for(j=0;j< f;j++)
  printf("%d \t",a[j]);
  printf("\n\n");
 }
 printf("no of page faults are %d",pf);
 getch();
}

First In First Out program using C (F.I.F.O)

#include< stdio.h>
#include< conio.h>
void main()
{
 int page[20],n,f,i,j,a[20],pf=0,k=0,match;
 clrscr();
 printf("enter the length of the reference string");
 scanf("%d",&n);
 printf("enter the frame size");
 scanf("%d",&f);

 printf("enter reference string");
 for(i=0;i< n;i++)
 scanf("%d",&page[i]);
 for(j=0;j< f;j++)
 a[j]=-1;

 printf("\n-1\t-1\t-1\n\n");

 k=0;
 for(i=0;i< n;i++)
 {
  match=0;
  for(j=0;j< f;j++)
  if(a[j]==page[i])
  {
   match=1;
  }
  if(match==1)
  {
   goto x;
  }

  for(j=0;j< f;j++)
  if(a[j]==-1)
  {
   a[j]=page[i];
   pf++;
   goto x;
  }

  a[k]=page[i];
  k=(k+1)%f;
  pf++;
  x:;
  for(j=0;j< f;j++)
  printf("%d \t",a[j]);
  printf("\n\n");
 }
 printf("no of page faults are %d",pf);
 getch();
}

Least Recently Used program using C(L.R.U)

#include< stdio.h>
#include< conio.h>
void main()
{
 int page[20],n,f,i,j,a[20],pf=0,match,index,counter=0,count[20];
 clrscr();
 printf("enter the length of the reference string");
 scanf("%d",&n);
 printf("enter the frame size");
 scanf("%d",&f);

 printf("enter reference string");
 for(i=0;i< n;i++)
 scanf("%d",&page[i]);
 for(j=0;j< f;j++)
 a[j]=-1;

 printf("\n-1\t-1\t-1\n\n");

 for(i=0;i< n;i++)
 {
  match=0;
  for(j=0;j< f;j++)
  if(a[j]==page[i])
  {
   match=1;
   counter++;
   count[j]=counter;
  }
  if(match==1)
  {
   goto x;
  }

  for(j=0;j< f;j++)
  if(a[j]==-1)
  {
   a[j]=page[i];
   counter++;
   count[j]=counter;
   pf++;
   goto x;
  }

  index=0;
  for(j=0;j< f;j++)
  {
   if(count[j]< count[index])
   {
    index=j;
   }
  }
  a[index]=page[i];
  counter++;
  count[index]=counter;
  pf++;
  x:;
  for(j=0;j< f;j++)
  printf("%d \t",a[j]);
  printf("\n\n");
 }
 printf("no of page faults are %d",pf);
 getch();
}

Bit stuffing of data using C

#include< stdio.h>
#include< conio.h>
#include< string.h>
void main()
{
    int i,j,a=0;
    char sdata[17],stuff[40],rdata[17];
    clrscr();
    printf("Enter the data in the form of 16 bits     : ");
    gets(sdata);
    printf("\nSender frame                              : ");
    puts(sdata);
    for(i=0,j=0;j <16;j++)
    {
        if(sdata[j]=='1')
        {
            a=a+1;
            if((a==5)&&(sdata[j+1]=='0'))
            {
                stuff[i]=sdata[j];
                i++;
                stuff[i]='0';
                a=0;
                i++;
            }
            else if(a==6)
            {
                stuff[i]='0';
                a=0;
                i++;
                j--;
            }
            else
            {
                stuff[i]=sdata[j];
                i++;
            }
        }
        else
        {
            stuff[i]=sdata[j];
            i++;
            a=0;
        }
    }
    stuff[i]='\0';
    printf("\nSender frame with bit stuffed             : ");
    puts(stuff);
    a=0;
    i=0;
    for(j=0;stuff[j]!='\0';j++)
    {
        if(stuff[j]=='1')
        {
            a=a+1;
            if(a==5)
            {
                a=0;
                rdata[i]=stuff[j];
                j++;
                i++;
            }
            else
            {
                rdata[i]=stuff[j];
                i++;
            }
        }
        else
        {
            a=0;
            rdata[i]=stuff[j];
            i++;
        }
    }
    rdata[i]='\0';
    printf("\nThe reciever data  without stuffed bit is : ");
    puts(rdata);
    if(strcmp(sdata,rdata)==0)
    printf("\nTransmission successful");
    else
    printf("\nTransmission error");
    getch();
}

Character stuffing of data using C

#include< stdio.h>
#include< conio.h>
#include< string.h>
void main()
{
    char sdata[17],rdata[17],cstuff[40];
    int i,j;
    clrscr();
    printf("Enter any 16 characters   : ");
    gets(sdata);
    printf("\nOriginal data             : %s\n",sdata);
    for(i=0,j=0;sdata[i]!='\0';i++)
    {
    if(sdata[i]=='f'&&sdata[i+1]=='l'&&sdata[i+2]=='a'&&sdata[i+3]=='g')
    {
        cstuff[j++]='e';
        cstuff[j++]='s';
        cstuff[j++]='c';
        cstuff[j++]=sdata[i];
    }
    else if(sdata[i]=='e'&&sdata[i+1]=='s'&&sdata[i+2]=='c')
    {
        cstuff[j++]='e';
        cstuff[j++]='s';
        cstuff[j++]='c';
        cstuff[j++]=sdata[i];
    }
    else
    {
        cstuff[j++]=sdata[i];
    }
    }
    cstuff[j]='\0';
    printf("\nAfter character stuffing  : %s\n",cstuff);
    for(i=0,j=0;cstuff[i]!='\0';i++)
    {
    if(cstuff[i]=='e'&&cstuff[i+1]=='s'&&cstuff[i+2]=='c')
    {
        i=i+3;
        rdata[j++]=cstuff[i];
    }
    else
    {
        rdata[j++]=cstuff[i];
    }
    }
    rdata[j]='\0';
    printf("\nReceiver data             : %s",rdata);
    if(strcmp(sdata,rdata)==0)
    printf("\n\n\nTransmission successful");
    else
    printf("\n\n\nTransmission error");
    getch();
}

Cyclic Redundancy check Using C

#include< stdio.h>
#include< conio.h>
#include< string.h>


char I[40],d[40]="1100000001011";
char a[12]="000000000000",t[13];
int i=0,j,l,n,p;


void main()
{
    void division(void);
    clrscr();
    printf("\n enter a message string    : ");
    gets(I);
    n=strlen(I);
    printf("\nOriginal message             : %s \n",I);
    strcat(I,a);
    p=n+12;
    division();
    printf("\nThe reminder at sender is : %s \n",t);
    for(i=n,j=1;i     {
    I[i]=t[j];
    }
    printf("\nThe padded string to be sent : %s \n",I);
    division();
    printf("\nThe remainder string at receiver : %s\n",t);
    printf("\nThe received message is correct");
    getch();
}

void division(void)
{
    for(i=0;i <13;i++)
    t[i]=I[i];
    while(i    {
    for(l=0;l <13;l++)
    {
        if(t[l]==d[l])
         t[l]='0';
        else
         t[l]='1';
    }
    if(t[0]=='0')
    {
        for(j=0;j <12;j++)
         t[j]=t[j+1];

        t[j]=I[i++];
    }
    }
    while(t[0]=='1')
    for(l=0;l <13;l++)
    {
    if(t[l]==d[l])
        t[l]='0';
    else
        t[l]='1';
    }
    t[l]='\0';
}

#include < stdio.h >
#include < conio.h >

void main()
{

int a[20],c[20],page[20];
int i,j,k,f,n;
int count=0;fault=0,hit=0;
clrscr();
printf("Enter reference string length : ");
scanf("%d",&n);
printf("Enter reference string");
for(i=0;i < n;i++)
   scanf("%d",&page[i]);
printf("Enter frame size ");
scanf("%d",&f);

for(i=0;i < f;i++)
{
   for(j=0;j < fault;j++)
   {
      if(page[i]==a[j])
      {
         hit++;
         c[j]=++count;
         goto xyz;
      }
    }
    a[i]=page[i];
    fault++;
    c[i]=++count;
    xyz: ;
}

Round Robin program using C

#include < stdio.h >
#include < conio.h >

void main()
{

 int  t1=0,wt,twt=0,tat=0,n,i,j,tq,c=0;
 int  bt[10],a[10],f[10],b[10];
 clrscr();
 printf("\n enter no of process: ");
 scanf("%d",&n);

 for(i=0;i < n;i++)
 {
    f[i]=0;    /* indicates process is completed if f[i]==1 */

    a[i]=i+1;    /*  indicates process names    */
 }

 for(i=0;i < n;i++)
 {
     printf("Enter the Burst time of process %d ",i+1);
     scanf("%d",&bt[i]);
     b[i]=bt[i];
 }


 printf("enter the time quantum : ");
 scanf("%d",&tq);

 printf("given burst times are:\n");

 for(i=0;i < n;i++)
 {
    printf("%d\t",bt[i]);
 }
 i=0;

 while(c < n)
 {
    if(bt[i]<=tq && f[i]==0)
    {
    t1=t1+bt[i];
    printf("\n turn around time of p%d is :  %d",a[i],t1);
    wt=t1-b[i];
    printf("\n Waiting time of p%d is     :  %d",a[i],wt);

    tat=tat+t1;
    twt=twt+wt;
    f[i]=1;
    c++;              /* indicating how many processes are completing  */

    }
    else
    {
    if(f[i]==0)
    {
        bt[i]=bt[i]-tq;
        t1=t1+tq;
    }
    }

    i=(i+1)%n;      */    for rotating value of   */
 }

 printf("\n\n Avg turn around time is   :  %d\n",tat/n);

 printf("\n\n Avg Waiting time is       :  %d",twt/n);

 getch();

}




Output:


Enter no of process : 3
Enter the Burst time of process 1 : 20
Enter the Burst time of process 2 : 5
Enter the Burst time of process 3 : 3

Enter time quantum : 4

Given burst times are :
20  5  3

turn around time of p3 is : 11
      Waiting time of p3 is : 8

turn around time of p2 is : 16
      Waiting time of p2 is : 11

turn around time of p1 is : 28
      Waiting time of p1 is :8

 Avg turn arround time is : 18
Avg waiting time is : 9

Program for Prime numbers

1.

main()
{
int a,c=0,i,n;
printf("enter the number to be checked");
scanf("%d",&n);
for(i=1;i<=n;i++)
   {
     a=n%i;
     if(a=0)
        {
           c=c+1;
        }
    }
if (c=2)
  { printf("the given number is prime"); }
else
    printf("the given number is not prime");
}

2.

main()
{
int i,j=2,ch=0;
clrscr();
       printf("\nENTER ANY NUMBER");
       scanf("%d",&i);
  while(j<=i/2)
       {
        if(i%j==0)
          {
            printf("%d IS NOT PRIME",i);
            ch=1;
            break;
          }
        else
          {
           j++;
          }
      }
 if(ch==0)
   {
   printf("%d IS PRIME",i);
   }
}

Fibonacci program using C

This program prints the Fibonacci series

#include
#include
void main(void)
{
    int i,j,k,n;
    clrscr();
    i=0;
    j=1;
    printf("%d    %d    ",i,j);
    for(n=0;n<=5;n++)
    {
    k=i+j;
    i=j;
    j=k;
    printf("%d    ",k);
    }
    getch();
}

RSA algorithm using C

/* C program for the Implementation Of RSA

Algorithm */

#include< stdio.h>

#include< conio.h>

int phi,M,n,e,d,C,FLAG;

int check()

{

int i;

for(i=3;e%i==0 && phi%i==0;i+2)

{

FLAG = 1;

return;

}

FLAG = 0;

}

void encrypt()

{

int i;

C = 1;

for(i=0;i< e;i++)

C=C*M%n;

C = C%n;

printf("\n\tEncrypted keyword : %d",C);

}

void decrypt()

{

int i;

M = 1;

for(i=0;i< d;i++)

M=M*C%n;

M = M%n;

printf("\n\tDecrypted keyword : %d",M);

}

void main()

{

int p,q,s;

clrscr();

printf("Enter Two Relatively Prime Numbers\t: ");

scanf("%d%d",&p,&q);

n = p*q;

phi=(p-1)*(q-1);

printf("\n\tF(n)\t= %d",phi);

do

{

printf("\n\nEnter e\t: ");

scanf("%d",&e);

check();

}while(FLAG==1);

d = 1;

do

{

s = (d*e)%phi;

d++;

}while(s!=1);

d = d-1;

printf("\n\tPublic Key\t: {%d,%d}",e,n);

printf("\n\tPrivate Key\t: {%d,%d}",d,n);

printf("\n\nEnter The Plain Text\t: ");

scanf("%d",&M);

encrypt();

printf("\n\nEnter the Cipher text\t: ");

scanf("%d",&C);

decrypt();

getch();

}

/*************** OUTPUT *****************

Enter Two Relatively Prime Numbers : 7 17

F(n) = 96

Enter e : 5

Public Key : {5,119}

Private Key : {77,119}

Enter The Plain Text : 19

Encrypted keyword : 66

Enter the Cipher text : 66

Decrypted keyword : 19 */

Making a small password/login form in C

Well, here's a very simple program to write the entries into a file, using the unix/linux/bsd crypt() function to encrypt the password and getpass() function to get the password unix style (no keyboard echo, at all):

#include
#include
#include
#include

int main(int argc, char **argv){

char salt[2]; /* Salt for the crypt() function */
const char *salt_chars = "abcdefghijklmnopqrstuvwxyz" /* Range of character supported */
"ABCDEFGHIJKLMNOPQRSTUVWXYZ" /* as a value for salt in crypt() */
"0123456789";

char username[BUFSIZ], password1[BUFSIZ], /* Buffers for user input and comparison */
password2[BUFSIZ], *buf;
char filename[BUFSIZ]; /* Buffer for filename */
FILE *outfile; /* File handle */

/* Build salt */
srand(time(NULL));
salt[0] = salt_chars[rand() % 62];
salt[1] = salt_chars[rand() % 62];

/* Get the filename */
printf("Enter Password Filename: ");
scanf("%s", filename);

/* Get the username */
printf("Username: ");
scanf("%s", username);

do {

/* Get the password */
buf = getpass("Password: ");

/* Copy to a "stable" pointer */
sprintf(password1, "%s", buf);

/* Get the password */
buf = getpass("Enter Again: ");

/* Copy to a "stable" pointer */
sprintf(password2, "%s", buf);

/* See if the passwords are the same */
if(strcmp(password1, password2) != 0)
printf("\nPasswords do not match!\nTry again.\n\n");

} while(strcmp(password1, password2) != 0);

/* Encrypt the password */
buf = crypt(password1, salt);

/* Open the output file for append */
if((outfile = fopen(filename, "a+")) == NULL){

printf("\nFile error!\nAborting...\n");

} else {

/* Print the record to the file */
fprintf(outfile, "%s:%s\n", username, buf);

} /* End if */

/* Close the file */
fclose(outfile);

} /* End main() */



And here's how you would check it:



#include
#include
#include
#include

int main(int argc, char **argv){

char username[BUFSIZ], *password; /* User input buffers */
char buf[BUFSIZ]; /* File input buffer */
char *user_file, *pass_file; /* Buffers for values in file */
char filename[BUFSIZ]; /* Filename buffer */
FILE *infile; /* File handle */

/* Get the filename */
printf("Enter Password Filename: ");
scanf("%s", filename);

/* Get the username from the user */
printf("Username: ");
scanf("%s", username);

/* Get the password from the user */
password = getpass("Password: ");

/* Open the file */
if((infile = fopen(filename, "r")) == NULL){

printf("\nFile error!\nAborting...\n");

} else {

/* Loop throught the file */
while (!feof(infile)) {

/* Initialize with empty string */
buf[0] = '\0';

/* Read in one line */
fscanf(infile, "%s", buf);

/* If it's an empty line, continue */
if(strlen(buf) == 0) continue;

/* Point to the buffer */
user_file = buf;

/* Point to the delimiter in the buffer */
pass_file = strchr(buf, ':');

/* Change the delimiter to a nul character */
pass_file[0] = '\0';

/* Move to the next character */
pass_file++;

/* See if this matches the name the user entered */
if(strcmp(user_file, username) == 0){

/* See if the passwords match */
if(strcmp(crypt(password, pass_file), pass_file) == 0){

printf("Correct password...\n");

} else {

printf("Invalid password!\n\n");

} /* End if */

/* We found what we wanted; get out of loop */
break;

} /* End if */

} /* End while */

} /* End if */

/* Close the file */
fclose(infile);

} /* End main() */



That's basically all there is to it. I used the most basic form--there are better ways (using a variety of encryption algorithms--like ones using stronger encryption than 56 bit, like this one does). Keep in mind, you have to compile in the crypt shared library--like this using gcc:

gcc -lcrypt -o program_name program_name.c

Otherwise, it'll blow up when you run it (coredump).