Thread: Can anyone see any errors in this cipher code?

I have this program to turn in for an assignment, and need to know if it is indented properly and I also get some ascii symbols appear instead of the actual letters on the output side. Can anyone tell me if they see an issue, and if so what line?

THANKS

Code:

/*Author: John Puskar Description: Project 4
  Date:  December 10, 2012  */


#pragma   warning(  disable:4996) 
#include<stdio.h>
//for small letters only
int FindGCD(int no1,int no2);
int InvEuclid(int a,int N) {
int r0,r1,r2,q1,x0,x1,x2;
r0=N;
r1=a;
x0=1;
r2=r0%r1;
q1=r0/r1;
x1=-q1;


	while (r2){
		r0=r1;
		r1=r2;
		q1=r0/r1;
		r2=r0%r1;
		x2=x0-(q1*x1);
		x0=x1;x1=x2;
	}


	if (x0>0)
		return x0;
	else
		return (N+x0);
}
int main () {
char small[27],data[100],cipher[100],decipher[100];
int i=0,j=0,k1,k2,flag,count=0,temp;


	for (i;i<26;i++){
		small[i] = 'a'+i;
		//printf("%c",small[i]);
	}
printf("please enter the text message to encrypt\n");
scanf("%[^\n]s",data);
fflush(stdin);
//ask user to provide atleast two mapping
i=0;
	while(1){
		printf("\nplease enter the first key 1<k1<26 such that gcd of (k2,26)=1\n");   //first key is: 19
		scanf("%d",&k1);
		printf("\nplease enter the second key 1<k2<26\n ");      // second key is: 4
		scanf("%d",&k2);
		flag =FindGCD(k1,26);
	if (flag==1)
		break;
	else
		printf("\nPlease reenter the keys");
	}
	//ciphere the text and show it to the user
	while (1){
		temp = data[i];
		// printf("g%d",flag);
	if (temp==0)
		break;
		flag= data[i]-'a';
	if (flag>=0 && flag <=25){
		flag=(flag*k1) +k2;
		//printf("g%d",flag);
		flag= flag%26;
		cipher[i]=small[flag];
	}
	else{
		cipher[i]=data[i];
	}
	count++;
	i++;


	}
printf("\nthe encrypted string is\n ");
	while(j<i){
		printf("%c",cipher[j]);
		j++;
	}
printf("\n");
//decipher the ciphered text
// printf("c%d\n",count);
k1= InvEuclid(k1,26);
//printf("%d",k1);
i=0;
	for(i=0;i<count;i++){
		flag= cipher[i]-'a';
		//printf("%d",flag);
	if (flag>=0 && flag <=25){
		flag=(flag-k2)*k1;
		//printf("g%d",flag);
		flag= flag%26;
		decipher[i]=small[flag];
	}
	else{
		decipher[i]=data[i];
	}
	}
j=0;
printf("\nthe dencrypted string is\n ");
	while(j<i){
		printf("%c",decipher[j]);
		j++;
	}
	printf("\n");
	return 0;
}
int FindGCD(int no1,int no2){
int divd,divs,r;
	if (no1>no2){
		divd=no1;
		divs = no2;
	}
	else{
		divd= no2;
		divs=no1;
	}
r = divd%divs;
	while (r>0){
		divd= divs;
		divs= r ;
		r= divd%divs;
		if (r==1){
			return 1;
		}
	}
	if (r==0){
		return divs;
	}
return 0;
}

my problem is still not solved by correcting the indentation. I also do not see why paste as plain text matters either. I just don't understand why I am getting ASCII code 203 symbol in my output! This is what I need help with.

Ok is the indentation any better here?

Code:

#pragma   warning( disable:4996) 
#include<stdio.h>


//function
int FindGCD(int no1,int no2);


//for small letters only
int InvEuclid(int a,int N) {
	int r0,r1,r2,q1,x0,x1,x2;
	r0=N;
	r1=a;
	x0=1;
	r2=r0%r1;
	q1=r0/r1;
	x1=-q1;


	while (r2)
	{
		r0=r1;
		r1=r2;
		q1=r0/r1;
		r2=r0%r1;
		x2=x0-(q1*x1);
		x0=x1;x1=x2;
	}


	if (x0>0)
		return x0;
	else
		return (N+x0);
}
int main () {
	char small[27],data[100],cipher[100],decipher[100];
	int i=0,j=0,k1,k2,flag,count=0,temp;


	for (i;i<26;i++){
		small[i] = 'a'+i;
		//printf("%c",small[i]);
	}
	// ask user to input message
	printf("please enter the text message to encrypt\n");
	scanf("%[^\n]s",data);
	fflush(stdin);
	//ask user to provide at least two mapping
	i=0;
	while(1)
	{
		printf("\nplease enter the first key 1<k1<26 such that gcd of (k2,26)=1\n");   //first key is: 19
		scanf("%d",&k1);
		printf("\nplease enter the second key 1<k2<26\n ");      // second key is: 4
		scanf("%d",&k2);
		flag =FindGCD(k1,26);
		if (flag==1)
			break;
		else
			printf("\nPlease re-enter the keys");
	}
	//cipher the text and show it to the user
	while (1)
	{
		temp = data[i];
		// printf("g%d",flag);
		if (temp==0)
			break;
			flag= data[i]-'a';
		if (flag>=0 && flag <=25)
		{
			flag=(flag*k1) +k2;
			//printf("g%d",flag);
			flag= flag%26;
			cipher[i]=small[flag];
		}
		else
		{
			cipher[i]=data[i];
		}
		count++;
		i++;


	}
	// show encrypted text to the user
	printf("\nthe encrypted string is\n ");
	while(j<i)
	{
		printf("%c",cipher[j]);
		j++;
	}
	printf("\n");
	//decipher the ciphered text
	// printf("c%d\n",count);
	k1= InvEuclid(k1,26);
	//printf("%d",k1);
	i=0;
	for(i=0;i<count;i++)
	{
		flag= cipher[i]-'a';
		//printf("%d",flag);
	if (flag>=0 && flag <=25)
	{
		flag=(flag-k2)*k1;
		//printf("g%d",flag);
		flag= flag%26;
		decipher[i]=small[flag];
	}
	else
	{
		decipher[i]=data[i];
	}
	}
	j=0;
	// show user the de-encrypted string
	printf("\nthe de-encrypted string is\n ");
	while(j<i)
	{
		printf("%c",decipher[j]);
		j++;
	}
	printf("\n");
	return 0;
}
int FindGCD(int no1,int no2){
	int divd,divs,r;
	if (no1>no2)
	{
		divd=no1;
		divs = no2;
	}
	else
	{
		divd= no2;
		divs=no1;
	}
	r = divd%divs;
	while (r>0)
	{
		divd = divs;
		divs = r;
		r= divd%divs;
		if (r==1)
		{
			return 1;
		}
	}
		if (r==0)
		{
			return divs;
		}
	return 0;
}

I am using Visual Studio and this is the warning:

Warning 1 warning C4996: 'scanf': This function or variable may be unsafe. Consider using scanf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. c:\users\john\desktop\c+projects\projects\#4\p04\p 04\p04.cpp 46 1 P04

Above is the screen shot of the program. The output issue is always with the vowels it seems.

E(x) = Ax + B (mod N) <= ENCRYPTION FUNCTION
D(x) = A^-1(x – B) (mod N) <= DECRYPTION FUNCTION
Note: A and N must be coprime. This means they share no prime factors.
A^-1 is the inverse of A (mod N). This means A * A^-1 = 1 (mod N)

Recall that A and B are mathematical constants used to determine the “key” used by the Affine Cipher. The two parties exchanging information would agree upon a key upfront so they know how to encrypt and decrypt the messages mathematically. N is the size of the alphabet we are using. In cryptography, we typically remove all spaces, punctuation and case information from the letters. This means we must transform input files so that they do not contains these invalid characters. In essence, all message will become a series of lowercase letters, which gives us 26 unique symbols we need to deal with. This gives us an alphabet size of N = 26.

No one can find an issue here and point me in the right direction?

Originally Posted by Salem

Code:

97      k1= InvEuclid(k1,26);
(gdb) n
99      i=0;
(gdb) print k1
$9 = 11
(gdb) s
100      for(i=0;i<count;i++)
(gdb) 
102        flag= cipher[i]-'a';
(gdb) 
104      if (flag>=0 && flag <=25)
(gdb) print flag
$10 = 2
(gdb) s
106        flag=(flag-k2)*k1;
(gdb) 
108        flag= flag%26;
(gdb) print flag
$11 = -22

Beware of maths on negative numbers.

THANKS for your response. However math I am not the best student. Can you at least tell me what lines are the issue?