Adding String to an unknown-size array c++

Question

Im having some trouble with an Array in C++. See I want to let the user give the program an input in form of a String, and keep doing it until the user is satisfied. My input is working fine but when i want to store the strings in to an array im running in to some problems. I have to define a size for my array apparently? and is there a way to store the input in 2 or 3 different arrays (depending on the input, which i sort with some if-statements) of strings, and the print them out? My code looks something like this now..

string firstarray[10];
string secarray[10];

//The cin stuff here and reading strings from user-input

    if(MyCondition1){ 
for(int x = 0; x<=9;x++){ 
firstarray[x] = name;  
}

  if(MyCondition2){ 
    for(int x = 0; x<=9;x++){ 
    secarray[x] = name;  
    }

Is there a way to skip the 10-limit of an array? could it be like string

firstarray[];

?

What is the problem you are trying to solve with multiple arrays? A vector<string> firstArray; gets rid of the size constraint. — Captain Giraffe
– Captain Giraffe, Commented Feb 28, 2012 at 14:40
You do mean std::string, right? I mean, I don't see a using namespace anywhere... — Mr Lister
– Mr Lister, Commented Feb 28, 2012 at 14:40

Martin Hennings · Accepted Answer · 2012-02-28 14:56:27Z

You're looking for a std::list. Or better, a std::vector which lets you access elements by their position.

Both of them can be expanded dynamically.

using namespace std;

// looks like this:
vector<string> firstvector;

firstvector.push_back(somestring); // appends somestring to the end of the vector

cout << firstvector[someindex]; // gets the string at position someindex
cout << firstvector.back(); // gets the last element

About your second question:
You can of course create several arrays / vectors to put your strings in. Maybe even use a std::map of type map<key, vector<string>> where key can be an enum for the category (or a string, but enum is better).

You put a new value into one of the vectors:

tCategoryEnum category = eCategoryNone;
switch(condition)
{
  case MyCondition1:
    category = eCategory1;
    break;
  case MyCondition2:
    category = eCategory2;
    break;
  // ...
}
// check if a category was found:
if(category != eCategoryNone)
{
    categoryMap[category].push_back(name);
}

Then to output this, you can simply loop over each category and vector element

for(int i = 0; i < categoryMap.size(); i++)
  for(int j = 0; j < categoryMap[i].size(); j++)
    cout << categoryMap[i][j];

Motti · Accepted Answer · 2012-02-28 14:39:15Z

5

Have you considered using an std::vector<string> > ?

answered Feb 28, 2012 at 14:39

Motti

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2 Comments

Handsken Over a year ago

i have encounterd it in some google-result. But i thought that it was to "over do it", guess i was wrong. Can some one link a how-to?

Motti Over a year ago

@Handsken no way is this overdoing it, vectors are simpler to use than arrays. Look at Martin's example it should get you on the right track.

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