使用加密密钥进行简单加密

Question

I am doing simple encryption. I have function called encryption(string text, string encryption_key). It should replace text's a's with first letter of encryption_key, b's with second and so on. I am trying to solve this with ASCII values.

I'm not sure if I think this right but I have tried something like this:

void encryption(std::string text, std::string encryption_key){
    for(long unsigned int i=0; i< encryption_key.length();i++){
        char letter = encryption_key.at(i);
        for(char j = 'a'; j<='z'; j++){
            if(text.find(j) != std::string::npos){
                text.at(j)= letter;
            }
        }
    std::cout<<"Encrypted text: "<< text<<std::endl;
    }
}

I am getting "terminate called after throwing an instance of 'std::out_of_range' what(): basic_string::at: __n (which is 101) >= this->size() (which is 5) Press to close this window..."

Is the idea right that I try to go through the encryption key characters first and replace the characters (az) in the text?

Answer 1

Fix:

auto pos = text.find(j);
if(pos != std::string::npos) {
    text[pos] = letter;
}

Answer 2

The fix to your code is text.at(text.find(j)) = letter;

void encryption(std::string text, std::string encryption_key){
    for(long unsigned int i=0; i< encryption_key.length();i++){
        char letter = encryption_key.at(i);
        for(char j = 'a'; j<='z'; j++){
            if(text.find(j) != std::string::npos){
                text.at(text.find(j))= letter;
            }
        }
    std::cout<<"Encrypted text: "<< text<<std::endl;
    }
}

I belive however, the algorithm is wrong from what you've described.

EDIT: Without using libraries you can do:

void encryption(std::string text, std::string encryption_key)
{
    for (int i=0; i<text.length(); i++)
    {
        for (char ch = 'a'; ch<='z'; ch++)
        {
            if (text[i] == ch)
            {
                text[i] = encryption_key[ch-'a'];
                break;
            }
        }    
    }

    std::cout<<"Encrypted text: "<< text<<std::endl;
}

Answer 3

With using replace algorithm, you can simply do this. It will go through the text string and replace all occurrences of a particular letter with the corresponding value in the encryption_key . Here encryption_key contains encrypted values for all small letters.

void encryption(std::string text, std::string encryption_key){
    int j = 0;
    for(auto i = 'a'; i <= 'z'; i++) //text has only small letters
    {
        std::replace( text.begin(), text.end(), i, encryption_key.at(j)); 
        j++;
    }
    std::cout <<"Encrypted text: "<< text<<std::endl;   
}

See DEMO