RSA encryption/decryption in c

Question

i am trying to implement rsa algorithm using c program. it works well in most cases.But in some cases it does not encrypt and again decrypt back to same stage.for example: "--" after encryption and decryption changes to "ƒƒ" here is the code for encryption and decryption. help would be appreciated. thanks in advance

void encrypt(uChar state[16])
{
    long int pt,ct,key=e[0],k;
    i=0;
    while(i<=16)
    {
        pt=state[i];
        pt=pt-96;
        k=1;
        for (j=0;j<key;j++)
        {
            k=k*pt;
            k=k%n;
        }
    ct=k+96;
    state[i]=ct;
    i++;
    }
}

void decrypt(uChar state[16])
{
    long int pt,ct,key=d[0],k;
    i=0;
    while(i<=16)
    {
        ct=state[i]-96;
        k=1;
        for (j=0;j<key;j++)
        {
            k=k*ct;
            k=k%n;
        }
        pt=k+96;
        state[i]=pt;
        i++;
    }
}

Answer 1

You are indexing outside the bounds of the array with

while(i<=16)

You can index state[16] only up to 15 so (in both functions) it should be

while(i < 16)