Strings Code not Working

Question

Using the C++ language, the function LetterChanges(str) takes the str parameter being passed and modifies it using the following algorithm.

Replace every letter in the string with the letter following it in the alphabet (ie. c becomes d, z becomes a). Then capitalize every vowel in this new string (a, e, i, o, u) and finally return this modified string.

#include <iostream>
using namespace std;

string LetterChanges(string str) {

    // code goes here
    string str2 = "abcdefghijklmnopqrstuvwxyz";
    int j;
    for (int i = 0; str[i] != '\0'; i++) {

        for (j = 0; str2[j] != '\0'; j++) {

            if (str[i] == str2[j]) {

                str[i] = str2[j + 1];

            }
        }
    }
    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] == 'a') {
            str[i] = 'A';
        }
        else if (str[i] == 'e') {
            str[i] = 'E';
        }
        else if (str[i] == 'i') {
            str[i] = 'I';
        }
        else if (str[i] == 'o') {
            str[i] = 'O';
        }
        else if (str[i] == 'u') {
            str[i] = 'U';
        }
    }
    return str;
}
int main() {
    // keep this function call here
    cout << LetterChanges(gets(stdin));
    return 0;
}

I am trying to run this code but it is not giving the desire output please help..

Answer 1

The Function

Let's start with your first loop:

for (int i = 0; str[i] != '\0'; i++) {
    for (j = 0; str2[j] != '\0'; j++) {
        if (str[i] == str2[j]) {
            str[i] = str2[j + 1];
        }
    }
}

There are a couple things here. Firstly, we don't even need to deal with str2. Characters in C++ use ASCII encoding, meaning we can actually do something like str[i]++ to change an 'a' to a 'b' or an 'e' to an 'f', etc...

Also, I'd advise against using str[i] != '\0'. We're using the standard library strings instead of c-strings for a reason, so we might as well make our lives easier and use str.size(). Along these same lines, I'd suggest str.at(i) as opposed to str[i] as the former will do bounds checking for us.

Lastly, if you include cctype, then we can use the isalpha function to make sure we're only modifying alphabetic characters (no numbers or spaces, etc..).

Thus your first loop can become:

for (int i = 0; i < str.size(); i++) {
    if(isalpha(str.at(i)){
        if(str.at(i) == 'z') str.at(i) = 'a'; //special case
        else str.at(i)++;
    }
}

As far as your second loop, you don't even need it! We can actually incorporate everything straight into the first one. As long as we make sure to do the vowel modification after we've changed the individual letters.

A conversion from lowercase to uppercase can be done with some ASCII math as well. The difference between the lowercase and uppercase letters is 'A'-'a', so if we add that to any lowercase letter, it'll give us its uppercase version!

With all of this, we can modify your code to:

for (int i = 0; i < str.size(); i++) {
    if(isalpha(str.at(i)){ //Make sure it's a letter!
        if(str.at(i) == 'z') str.at(i) = 'a'; //special case
        else str.at(i)++;

        if(str.at(i) == 'a' | str.at(i) == 'e' | str.at(i) == 'i' 
           | str.at(i) == 'o' | str.at(i) == 'u') {
           str.at(i) += 'A' - 'a'; 
    }
}

Your Main

There's only one thing to fix here. Don't use gets for input. If you're looking for a single word, use the extraction operator, >>, or if you want a whole line, use getline.

string word, line;

getline(cin, line);
cin >> word;

cout << LetterChanges(line) << endl;
cout << LetterChanges(word) << endl;