How do I increment letters in c++?

Question

I'm creating a Caesar Cipher in c++ and i can't figure out how to increment a letter.

I need to increment the letter by 1 each time and return the next letter in the alphabet. Something like the following to add 1 to 'a' and return 'b'.

char letter[] = "a";
cout << letter[0] +1;

Solution 1

This snippet should get you started. letter is a char and not an array of chars nor a string.

The static_cast ensures the result of 'a' + 1 is treated as a char.

> cat caesar.cpp          
#include <iostream>

int main()
{
    char letter = 'a';
    std::cout << static_cast<char>(letter + 1) << std::endl;
}

> g++ caesar.cpp -o caesar
> ./caesar                
b

Watch out when you get to 'z' (or 'Z'!) and good luck!

Solution 2

It works as-is, but because the addition promotes the expression to int you want to cast it back to char again so that your IOStream renders it as a character rather than a number:

int main() {
   char letter[] = "a";
   cout << static_cast<char>(letter[0] + 1);
}

Output: b

Also add wrap-around logic (so that when letter[0] is z, you set to a rather than incrementing), and consider case.

Solution 3

You can use 'a'+((letter - 'a'+n)%26); assuming after 'z' you need 'a' i.e. 'z'+1='a'

    #include <iostream>

    using namespace std;

    int main()
    {
       char letter='z';
       cout<<(char)('a' + ((letter - 'a' + 1) % 26));

       return 0;
    }

See this https://stackoverflow.com/a/6171969/8511215

Solution 4

Does letter++ work? All in all char is a numeric type, so it will increment the ascii code. But I believe it must be defined as char letter not an array. But beware of adding one to 'Z'. You will get '[' =P

#include <iostream>

int main () {
    char a = 'a';
    a++;
    std::cout << a;
}

This seems to work well ;)

Solution 5

waleed@waleed-P17SM-A:~$ nano Good_morning_encryption.cpp waleed@waleed-P17SM-A:~$ g++ Good_morning_encryption.cpp -o Good_morning_encryption.out waleed@waleed-P17SM-A:~$ ./Good_morning_encryption.out Enter your text:waleed Encrypted text: jnyrrq waleed@waleed-P17SM-A:~$ cat Good_morning_encryption.cpp

    #include <iostream>
    #include <string>

    using namespace std;


    int main() {

    //the string that holds the user input
    string text;
    //x for the first counter than makes it keeps looping until it encrypts the user input
    //len holds the value (int) of the length of the user input ( including spaces)
    int x, len;

    //simple console output
    cout << "Enter your text:";
    //gets the user input ( including spaces and saves it to the variable text
    getline(cin, text);
    //give the variable len the value of the user input length
    len = (int)text.length();
    //counter that makes it keep looping until it "encrypts" all of the user input (that's why it keeps looping while its less than len
    for(x = 0; x < len; x++) {
    //checks each letts (and spaces) in the user input (x is the number of the offset keep in mind that it starts from 0 and for example text[x] if the user input was waleed would be w since its text[0]
    if (isalpha(text[x])) {
    //converts each letter to small letter ( even though it can be done another way by making the check like this if (text[x] =='z' || text[x] == 'Z')
    text[x] = tolower(text[x]);
    //another counter that loops 13 times
    for (int counter = 0; counter < 13; counter++) {

    //it checks if the letts text[x] is z and if it is it will make it a
    if (text[x] == 'z') {

    text[x] = 'a';

    } 
    //if its not z it will keeps increamenting (using the loop 13 times)
    else {


    text[x]++;

    }

    }
    }
    }
//prints out the final value of text
    cout << "Encrypted text:\n" << text << endl;
    //return 0 (because the the main function is an int so it must return an integer value
    return 0;

    }

Note: this is called caeser cipher encryption it works like this :

ABCDEFGHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM so for example my name is waleed it will be written as : JNYRRQ so its simply add 13 letters to each letter

i hope that helped you

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Comments

[Linus Kleen]

This just outputs a and afterwards increments letter.

[Lightness Races in Orbit]

Why would you cast before incrementing?

[Roee Gavirel]

Yeah, fix it. (-1 it's kinda harsh, isn't it?)

[Linus Kleen]

I'd like to remove my -1 but it's locked now unless the answer is edited :-(

[Sammy S.]

There is no such type in C or C++ ... You're thinking of Java or C# right now.

[deW1]

Caesars Chiffre is +3 not +13 btw.

[saagarjha]

This relies on implementation defined behavior, since C and C++ don't guarantee that the alphabetical characters are contiguous.

[johnsyweb]

Surely ASCII and Unicode standards have this covered?

[saagarjha]

Yes, it does, but C is designed to portable–this means it runs on computers that may not be fortunate enough to use ASCII or Unicode.

[Peter]

@Johnsyweb - Saagar Jha is correct. There are real-world standardised character sets, and C++ implementations that work with them. With such implementations, your solution will not work. For people who are willing to assume ASCII or Unicode your solution is fine, but such code will be a bug waiting to be exposed at run time (since it would not be diagnosed by a compiler) when ported to another system.