Can anyone see any errors in this cipher 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;
}

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];
		}
	}