C++ Check and modify strings / String subscript out of range - c++

Question

I'm trying to make a program which modifies words in a specific manner:
It should first check the ending of the words and then proceed to modify them. I won't explain it in detail, because it doesn't make much sense in English.
I've written the following:
#include "stdafx.h"
#include <iostream>
#include <string>
using namespace std;
int main()
{
cout << "Por favor, introduzca los gentilicios separados por la tecla enter, para finalizar, escriba OK" << '\n';
string name[10];
string place[10];
for (int i(0); (i < 10); i++)
{
getline(cin, name[i]);
if (name[i] == "OK") //Error here
break;
}
for (int i(0); (i < 10); i++)
{
place[i] = name[i];
if (name[i][name[i].length() - 1] == 'c')
{
if (name[i][name[i].length()] == 'a' || (name[i][name[i].length()] == 'o') || (name[i][name[i].length()] == 'u'))
place[i][place[i].length() - 1] = 'q';
place[i][place[i].length()] = 'u';
place[i] = place[i] + "istan";
}
else if (name[i][name[i].length()] == 'a' || name[i][name[i].length()] == 'e' || name[i][name[i].length()] == 'i' || name[i][name[i].length()] == 'o' || name[i][name[i].length()] == 'u')
{
place[i][place[i].length()] = 'i';
place[i] = place[i] + "stan";
}
if (name[i][name[i].length()] == 's')
place[i] = place[i] + "tan";
else {
place[i] = place[i] + "istan";
}
place[i][0] = toupper(place[i][0]);
}
for (int i(0); (i < 10); i++)
{
cout << place[i] << '\n';
}
return 0;
}
Now I'm getting the error "String subscript out of range" . I would like to know where is the error exactly. I know it prompts when I write "OK", at line "18".

Answer 1

The condition i <= sizeof(name). sizeof(name) returns the size of the array in bytes, not the number of elements in it. Even if it returned the number of elements, <= is wrong and would cause an out-of-bounds access (should be <).
To loop through all elements in an array, you can use the range-based for-loop:
for(auto& n : name)
{
getline(cin, n);
if (n == "OK")
break;
}
Or to do it the right way with the C-style for-loop:
for (int i(0); i < sizeof(name)/sizeof(name[0]; i++)
{
…
}

Answer 2

Here:
for (int i(0); (i <= sizeof(name)); i++)
sizeof(name) is the size in bytes of the array, which as it is an array of std::string is effectively meaningless. If you want to iterate over 10 items, simply say so (note also that less-than-or-equals is also wrong here):
for (int i = 0; i < 10; i++)
And here:
getline(cin, name[i]);
whenever you perform input you must check the return value of the input function and handle any errors:
if( ! getline(cin, name[i]) ) {
// handle error somehow
}
And here:
string * p;
you do not want to be dealing with pointers to strings. If you want to access the contents of a string, you use operator[] or other string member functions on the string.

Answer 3

std::strings are not like cstrings. You can just grab a part of them using a std::string*. When you do
*(p+ (name[i].length()-2))
You actually say advance the address stored in p by name[i].length()-2 amount and access that string. If you go past the end of the name array then that is undefined behavior. If not you still haver a std::string which cannot be compared with a char. If you want to check if the string ends with "ca" then you can just use
if (name[i].substr(name[i].size() - 2) == "ca")

Answer 4

You're last loop is doing something quite funky. There's no need to go that far. You can just do something like:
if (name[i][name[i].length - 2] == 'c')
To compare the next to last character with c. And a very similar test to compare the last one with a.
To clarify why what you're doing is not OK, you first get p as a pointer to a string to the current element. Then you do some pointer arithmetic p + (name[i].length - 2), which still results in a pointer to a string. Finally, you dereference this, resulting in a string. Which you can't compare to a char. Moreover, the pointer was to some arbitrary address in memory, so the dereference would produce a string with very bad data in it. Quite arbitrary, one might say. If you tried to work with it you'd break your program
You seem to be working with the string as one would with a C-like string, a char*. The two are not the same, even though they represent the same concepts. A C++ string, usually, has a size field, and a char* pointer inside it, as well as a bunch of other logic to make working with it a char-m.

Answer 5

Because you aren't comparing against a specific char in the string, you're comparing against a string.
Considering the following bit of code:
*(p + (name[i].length() - 2))
This evaluates to a string because you are taking p (a string*) and concatenating a char to it. This means it's still a string (even though it's a one-character string), thus the other side of the equation won't be comparable to it.
What you need here instead is this:
if (name[i][name[i].length() - 2] == 'c')
Since name[i] is already a string, we can just get the char from it using the code above. This does return char, so it's comparable. This also allows you to get rid of the whole string* bit as it is not needed.

Answer 6

First, (i <= sizeof(name)) is wrong, it should be i < sizeof(name) / sizeof(*name). sizeof(array) return the size of array in bytes, you need to divide the size of an array's element to actually get the maximum element count of an array. If you find that complicated then use std::vector:
vector<string> name(10); //a vector of size 10
for (size_t i = 0; i < name.size(); i++) //name.size(), simple
Secondly, you need to keep track of how many strings in your name array. Or you need to check if name[i] == "OK" then break the second loop (similar to the first loop). name[i] after "OK" are invalid.
Thirdly, don't use *(p+ (name[i].length()-2)). If you want the second last character of name[i], you can write it as name[i][name[i].size()-2] or name[i].end()[-2] or end(name[i])[-2]
If you want to check if the word ends in "ca", then you can use substr:
if (name[i].substr(name[i].size() - 2) == "ca")
{
//...
}