Python,C,C++ and JAVA programs for CBSE, ISC, B.Tech and I.T Computer Science and MCA students

The Programming Project: 2012

Sunday, December 16, 2012

Deletion of text inside brackets : C Code


C program to read a string and remove anything written inside closed brackets '(' ,')':

#include<stdio.h>
int main()
{
char s[200],temp;
int l,i=0,flag=1,j;
printf("\n Enter the string:");
do
      {
       s[i]=getchar();
       }
       while(s[i++]!='\n');
       s[i]='\0';
       i=0;
       while(s[i]!='\0')
       {

        if(s[i]=='(')
                  {
                  while(s[i]!=')')
                  ++i;
                  }
     if(s[i]!=')')   
        printf("%c",s[i]);
     i++;
        }
      return 0;
}
INPUT/OUTPUT:
Enter the string:amhjdg (dshjg)(dbh)hjdv dgfv (a)
OUTPUT: amhjdg hjdv dgfv

C Program #6


/* program to write a sentence is one file and print the entire sentence
to the second file by reversing the non palindrome word only*/
#include<stdio.h>
#include<string.h>
int palin(char c[15]);
int main()
{
FILE *fp,*fq;
char c='a',ct[15];
int i,len,j;
fp=fopen("first.txt","w");
if(fp==NULL)
      {
      printf("\n ERROR opening file:");
      }
else
      {
      printf("\n Enter the text:");
      while(c!='\n')
            {
      scanf("%c",&c);
            fprintf(fp,"%c",c);
            }
      }
fclose(fp);
fq=fopen("first.txt","r");
fp=fopen("second.txt","w");
if(fq==NULL)
      {
      printf("\n ERROR opening file:");
      }
else
      {
      while(!feof(fq))
            {
                  i=0;
                  c=fgetc(fq);
                  while(c!=' ' && c!='\n')
                        {
                        ct[i]=c;
                        i++;
                        c=fgetc(fq);
                        if(c==EOF)break;
                        }ct[i]='\0';
                  if(palin(ct)==0)
                        {
                        fputs(ct,fp);
                        fputc(' ',fp);
                        }
                  else
                        {
                        len=strlen(ct);
                        for(j=len-1;j>=0;j--)
                              {
                        fputc(ct[j],fp);
                              }
                        fputc(' ',fp);
                        }

            }
      }
fcloseall();
fp=fopen("second.txt","r");
      if(fp==NULL)
                  printf("\n ERROR OPENING FILE:");
      else
                  {
         printf("\n Text is the second file:\n");
                  while(!feof(fp))
                        {
                        fscanf(fp,"%c",&c);
                        printf("%c",c);
                        }
                  }
fcloseall();
return 0;
}
int palin(char c[])
{
int len,i,j=0;
char p[15];
len=strlen(c);
for(i=len-1;i>=0;i--)
      {
      p[j]=c[i];
      j++;
      }
      p[j]='\0';
      if(strcmp(p,c)==0)
            return 0;
            else
                  return 1;

}

C Program #5



/* Program to reverse the alternate words of a string */
#include<stdio.h>
#include<string.h>
void reverse(char rev[],int n);
int main()
{
char str[100],rev[10];
int len,i,j,count;
printf("\n Enter a string:");
gets(str);
len=strlen(str);
printf("\n Converted string is:\n");
for(i=0;i<len;i++)
      {
       printf("%c",str[i]);
       if(str[i]==' ')
            {

                  j=i;
                  count=0;
                  while(str[++j]!=' ')
                        {
                        rev[count]=str[j];
                        count ++;
                        }
                        reverse(rev,count);
                        i=j;
            putc(' ',stdout);
                  }

       }
      return 0;
}
void reverse(char rev[],int n)
{
 int i;
      for(i=n-1;i>=0;i--)
            printf("%c",rev[i]);
}
INPUT/OUTPUT:
Enter a string:Program to reverse the alternate words of a string

 Converted string is:
Program ot reverse eht alternate sdrow of a string 

Saturday, December 15, 2012

RSA Encryption : C Code

RSA is an algorithm for public-key cryptography that is based on the presumed difficulty of factoring large integers, the factoring problem. RSA stands for Ron Rivest, Adi Shamir and Leonard Adleman, who first publicly described it in 1977. Clifford Cocks, an English mathematician, had developed an equivalent system in 1973, but it was classified until 1997. A user of RSA creates and then publishes the product of two large prime numbers, along with an auxiliary value, as their public key. The prime factors must be kept secret. Anyone can use the public key to encrypt a message, but with currently published methods, if the public key is large enough, only someone with knowledge of the prime factors can feasibly decode the message.Whether breaking RSA encryption is as hard as factoring is an open question known as the RSA problem. Below is the C program to demonstrate the algorthm (using small prime numbers, not suitable for real life application)

#include<iostream.h>
#include<math.h>
#include<string.h>
#include<conio.h>
#include<stdio.h>
#include<stdlib.h>
void keygen(void);
void ran(void);
void man(void);
void encrypt(void);
void decrypt(void);
int sqrmul(int,int,int);
int invr1(int,int);
int invr(int,int);
int prime(int);
int gcd(int,int);
void main()
{
      int chk;
      do
      {
      printf("\n-------------------------------------------\n");
      printf("\n*MAIN MENU*");
      printf("\n");
      printf("\t \t \t \n *PROGRAM TO DEMONSTRATE RSA CIPHER         
      SYSTEM*");
      printf("\n--------------------------------------------\n");
      printf("\n Press 1 to ENCRYPT:");
      printf("\n Press 2 to DECRYPT:");
      printf("\n Press 3 to GENERATE KEY:");
      printf("\n Press 4 to EXIT:");
      printf("\n Please enter your choice......");
      scanf("%d",&chk);
      printf("\n");
      switch(chk)
            {
            case 1:
            encrypt();
            break;
            case 2:
            decrypt();
            break;
            case 3:
            keygen();
            break;
            case 4:
            break;
            default:
            printf("\n You have enter a wrong choice!!!!!!!!\n");
            break;
            }
      }
      while(chk!=4);
}

void encrypt()
{
      char pln[100];
      int len,e,n,tm;
      printf("\n Enter the plain text:");
      cin.getline(pln,'\100');
      printf("\n Enter the public key (e,n):");
      scanf("%d %d",&e,&n);
      len=strlen(pln);
      printf("\n The cipher text is:");
      for(int i=0;i<len;i++)
            {
             tm=pln[i];
             printf("%d ",sqrmul(tm,e,n));
             }
      printf("\n Length of cipher text is: %d",len);
      getche();
}
void decrypt()
{
int cip[50],e,n1,l;
printf("\n Enter the lenth:");
scanf("%d",&l);
printf("\n Enter d and n:");
scanf("%d %d",&e,&n1);
printf("\n Enter the cipher text:");
for(int i=0;i<l;i++)
scanf("%d",&cip[i]);
printf("\n The decoded message is: ");
for(int j=0;j<l;j++)
      {
      printf("%c",sqrmul(cip[j],e,n1));
      }
getche();
}
void keygen()
{
int ch;
do
      {
      printf("\n\n");
      printf("\nKEY GENERATOR FOR RSA");
      printf("\nPress 1 for random selection");
      printf("\nPress 2 for manual selection");
      printf("\nPress 3 to return to main menu\n\t\t");
      scanf("%d",&ch);
            switch(ch)
            {
            case 1:
            ran();
            break;
            case 2:
            man();
            break;
            case 3:
            break;
            default:
            printf("\n Wrong choice:");
            }
      }while(ch!=3);
}
void man(void)
{
int u,i,ar[1000],k=0,p,q,ph,n,e;
printf("\n Enter the upper limit:");
scanf("%d",&u);
printf("\n You can choose any two primes from the following prime(s):\n");
for(i=2;i<=u;i++)
      {
      if(prime(i)==1)
            {
            ar[k]=i;
            printf("\t%d(%d)",ar[k],k);
            k++;
            }
      }
printf("\n");
printf("\n Enter  two numbers between 0 and %d :",k-1);
scanf("%d %d",&p,&q);
printf("\n");
printf("\n Your choice of p and q is:%d %d",ar[p],ar[q]);
ph=(ar[p]-1)*(ar[q]-1);
n=(ar[p])*(ar[q]);
printf("\n");
printf("\n phi(%d) is: %d",ar[p]*ar[q],ph);
int z=0;
printf("\n");
printf("\n You can choose any one number for 'e':\n");
for(i=2;i<ph;i++)
      {
      if(gcd(i,ph)==1)
            {
            ar[z]=i;
            printf("\t%d(%d)",ar[z],z);
            z++;
            }
      }
printf("\n");
printf("\n Enter  one number between 0 and %d :",z-1);
scanf("%d",&e);
printf("\n");
printf("\n Your choice of e is:%d",ar[e]);
printf("\n");
printf("\n You have chosen the public key:(%d,%d)",ar[e],n);
printf("\n");
printf("\n Private key is: (%d,%d)",invr(ar[e],ph),n);
printf("\n Press any key............");
getche();
}
void ran()
{
int u,i,ar[400],k=0,p,q,ph,n,e;
printf("\n Enter the upper limit:");
scanf("%d",&u);
printf("\n p and q will be seleted automatically from the list below:\n");
printf("\n");
for(i=2;i<=u;i++)
      {
      if(prime(i)==1)
            {
            ar[k]=i;
            printf("\t%d",ar[k]);
            k++;
            }
      }
printf("\n");
p=rand()%k;
do
      {
      q=rand()%k;
      }while(q==p);
printf("\n");
printf("\n Selected value p and q is:%d %d",ar[p],ar[q]);
printf("\n");
ph=((ar[p]-1)*(ar[q]-1));
n=(ar[p])*(ar[q]);
printf("\n");
printf("\n phi(%d) is: %d",n,ph);
printf("\n");
int z=0;
printf("\n");
printf("\n e will be seleted automatically from the list below :\n");
printf("\n");
for(i=2;i<ph;i++)
      {
      if(gcd(i,ph)==1)
            {
            ar[z]=i;
            printf("\t%d",ar[z]);
            z++;
            }
      }
printf("\n");
e=rand()%z;
printf("\n");
printf("\n Selected e is:%d",ar[e]);
printf("\n");
printf("\n The public key:(%d,%d)",ar[e],n);
printf("\n");
printf("\n Private key is: (%d,%d)",invr(ar[e],ph),n);
printf("\n Press any key.........");
getche();
}
int prime(int n)
{
int i,rem,k=0;
for(i=2;i<=sqrt(n);i++)
      {
      rem=n%i;
      if(rem==0)
            {
            k++;
            }
      }
if(k>0)
return 0;
else
return 1;
}
int gcd(int a,int b)
{
int x,y,rem;
x=abs(a);
y=abs(b);
if(x<y)
{
int tmp=y;
y=x;
x=tmp;
}
do
{
rem=x%y;
x=y;
y=rem;
} while(rem!=0);
if(x==1)
return 1;
else
return 0;
}
int sqrmul(int p,int e,int n)
{
      unsigned long int rem,q,a[20],i=19,mod;
while(q!=1)
      {
      rem=e%2;
      q=(e-rem)/2;
      e=q;
      a[i]=rem;
      i--;
      }
      a[i]=1;
      long int k=0,tmp;
for(int j=i;j<20;j++)
{
      if(k==0)
      {
      mod=p%n;
      tmp=mod;
      }
      else
      {
            if(a[j]==1)
            {
            mod=(tmp*tmp*p)%n;
            tmp=mod;
            }
            else
            {
            mod=(tmp*tmp)%n;
            tmp=mod;
            }
      }

      k++;

}
return(tmp);

}
int invr(int a,int b)
{
long int temp=0,inv;
do
      {
      inv=a*temp-1;
      ++temp;
      }
       while(inv%b!=0);
       return (temp-1);
}
int invr1(int e,int n)
{
long int temp=0,inv;
do
      {
      inv=e*temp-1;
      ++temp;
      }
       while(inv%n!=0);
       return(temp-1);
}

Sum of even numbers of an array using recursion : C Code


To find the sum of even numbers of an array using recursion.
/* to calculate the sum of even numbers using recursion */
#include<stdio.h>
#include<malloc.h>
int evensumrec(int *a,int n);
int main()
{
int *a,i,n,sum;
printf("\n Enter the number of elements:");
scanf("%d",&n);
a=(int *)malloc(n*sizeof(int));
printf("\n Enter the elements of the array:");
for(i=0;i<n;i++)
      scanf("%d",(a+i));
      sum=evensumrec(a,n-1);
printf("\n Sum of even numbers is %d",sum);
return 0;
}
int evensumrec(int *a, int n)
{
      if(*(a+n)%2==0)
            {
            if(n>=0)
                  return (*(a+n)+evensumrec(a,n-1));
            else
                  return 0;
            }
       else
            return (evensumrec(a,n-1));
}

Input/Output:
 Enter the number of elements:7

 Enter the elements of the array:23
4
-6
13
17
66
0

 Sum of even numbers is 64

Sorting of words in a String : C Code


Program to sort the words of a string

/* To sort the words of an input string */
#include<stdio.h>
#include<string.h>
#include<malloc.h>
int main()
{
char str[40],*x[10],*temp;
int i=0,j=0,len,t,k,l,tmp;
printf("\n Enter a string:");
gets(str);
len=strlen(str);
for(i=0;i<=len;i++)
      {
      k=i;
      tmp=0;
      while(str[k]!=' ' && str[k]!='\0')
            {
            k++;
            tmp++;
            if(str[i]=='\n')
            break;
            }
            x[j]=(char *)malloc(tmp*sizeof(char));
            l=0;
                  for(t=i;t<tmp+i;t++)
                  {
                        *(x[j]+l)=str[t];
                        l++;
                  }
                  *(x[j]+l)='\0';
            i=k;
            j++;
            }
for(i=0;i<j-1;i++)
      {
            for(k=i+1;k<j;k++)
                  {
                  if(strcmp(x[i],x[k])>0)
                        {
                        temp=x[k];
                        x[k]=x[i];
                        x[i]=temp;
                        }
                  }
      }
puts("\n Sorted words of the string:\n");
for(i=0;i<j;i++)
      printf("%s\n",x[i]);
return 0;
}



Input/Output:

Enter a string:sorting of the words in a string

 Sorted words of the string:

a
in
of
sorting
string
the
words


Second largest word of a input string

A simple C program to print the second largest word of a input string using array of pointers

/* to find the second largest word in the sentence and to print it */
#include<stdio.h>
#include<string.h>
#include<malloc.h>
int main()
{
char str[40],*x[10];
int i=0,j=0,tmp,len,t,k,l,leng[20];
printf("\n Enter a string:");
gets(str);
len=strlen(str);
for(i=0;i<=len;i++)
      {
      k=i;
      tmp=0;
      while(str[k]!=' ' && str[k]!='\0')
            {
            k++;
            tmp++;
            if(str[i]=='\n')
            break;
            }
            x[j]=(char *)malloc(tmp*sizeof(char));
            l=0;
                  for(t=i;t<tmp+i;t++)
                  {
                        *(x[j]+l)=str[t];
                        l++;
                  }
                  *(x[j]+l)='\0';
            i=k;
            j++;
            }
for(i=0;i<j;i++)
      {
       leng[i]=(strlen(x[i]));
            //printf("\n [%d] %s",leng[i],x[i]);
      }
for(i=0;i<j-1;i++)
      {
            for(k=i+1;k<j;k++)
                  {
                  if(leng[i]<leng[k])
                        {
                        tmp=leng[k];
                        leng[k]=leng[i];
                        leng[i]=tmp;
                        }
                  }
      }
tmp=leng[1];
if(tmp==leng[0])
      {
      for(i=0;i<j;i++)
            {
            if(tmp==leng[i])
            continue;
            else
                  {
                  tmp=leng[i];
            break;
                  }
            }
      }
puts("\n Second longest words is/are:");
for(i=0;i<j;i++)
      {
            if(tmp==strlen(x[i]))
            printf(" %s ",x[i]);
      }

return 0;
}