Having trouble adding an element to a string vector [closed]

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Closed 8 years ago.

I'm writing a simple journal like function, however I can't seem to fathom out how to generate a new element of the vector by passing the value the user enters. I am new to programming so the answer might well be obvious :/ I get no errors when I compile the program but the code for adding in a journal entry seems to have no effect. Any ideas?

This is the program below:

#include <iostream>
#include <string>
#include <vector>

using namespace std;

int main()

{
    bool running = true;

    while (running = true) 
    {

    vector<string> journal;
    vector<string>::const_iterator iter;
    int count = 1;

    journal.push_back("Day 1. Found some beans.");
    journal.push_back("Must remember not to eat beans");
    journal.push_back("Found some idiot who traded beans for a cow!");

    cout << "Journal Tester.\n\n";


    cout << "1 - View Journal\n2 - Add journal entry\n";
    cout << "3 - Quit\n";
    cout << "\nPlease choose: ";

    string newentry;
    int choice; 
    cin >> choice;
    cout << endl;

    switch (choice)
    {
    case 1:
        for (iter = journal.begin(); iter != journal.end(); ++iter)
    {

        cout << "Entry " << count << ": \n";
        cout << *iter << endl; 
        ++ count;
    }
        count = 1;
        break;

    case 2: 

        cout << "\nYou write: ";
        cin >> newentry; 

        cout << endl << newentry;
        journal.push_back(newentry); 

        break;

    }

    } 

    return 0;
}

Answer 1

This:

vector<string> journal;

is recreated on each iteration of the while loop so when the code that prints the elements operates on a new empty vector. Move the definition of journal to outside of the while loop:

vector<string> journal;
while (running) // Note removed assignment here.
{
}

And the hardcoded values that are push_back()ed into the vector may also need to moved outside of the loop if you do not want these repeatedly added.

Answer 2

The vectors are declared inside the "while" loop, so they are local to it, and get created anew for each iteration of the loop. That means the program forgets its own past every time around. Move the vector declarations before the loop and things will improve greatly!

Answer 3

It's because your vector variable is instantiated inside the scope of the while loop. That means it is newly created in every turn of the loop, the data that was added with case 2: of the switch statement is lost.

Answer 4

    #include <iostream>
    #include <string>
     #include <vector>

     using namespace std;
 vector<string> journal;//**SHOULD NOT WRITE INSIDE THE LOOP**
 int main()

  {
bool running = true;

while (running = true) 
{


vector<string>::const_iterator iter;
int count = 1;

journal.push_back("Day 1. Found some beans.");
journal.push_back("Must remember not to eat beans");
journal.push_back("Found some idiot who traded beans for a cow!");

cout << "Journal Tester.\n\n";


cout << "1 - View Journal\n2 - Add journal entry\n";
cout << "3 - Quit\n";
cout << "\nPlease choose: ";

string newentry;
int choice; 
cin >> choice;
cout << endl;

switch (choice)
{
case 1:
    for (iter = journal.begin(); iter != journal.end(); ++iter)
{

    cout << "Entry " << count << ": \n";
    cout << *iter << endl; 
    ++ count;
}
    count = 1;
    break;

case 2: 

    cout << "\nYou write: ";
    cin >> newentry; 

    cout << endl << newentry;
    journal.push_back(newentry); 

    break;

}

} 

return 0;

}

Answer 5

create vector once only, before loop:

vector<string> journal;
while (running) // <- also change this to avoid inf loop
{
 string s("me");
 journal.push_back(s);
 //.. do things with your vector "journal"
}

alse be careful what you do in loop.