Error while adding elements to vector

Question

I'm trying to add element in the vector. I want to add all even numbers from 10 to 21. But I'm getting the error. Can someone please tell me how to fix it.

int main()
{
vector<int> vect_name;
for (int i=10; i<21; i=i+2)
    vect_name.push_back(i);
    cout << vect_name[i] <<endl;

return 0;

}

Please [read about how to ask good questions](http://stackoverflow.com/help/how-to-ask), and learn how to create a [Minimal, **Complete**, and Verifiable Example](http://stackoverflow.com/help/mcve). — Some programmer dude, Oct 26 '17 at 04:15
You should probably also [get a couple of good beginners books](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) to read, and learn about *scoping* and the use of curly-brackets `{}`. — Some programmer dude, Oct 26 '17 at 04:16
Here is my error (if you use ‘-fpermissive’ G++ will accept your code) — rida, Oct 26 '17 at 04:19
When adding information, please *edit your question*. Don't post comments. — Some programmer dude, Oct 26 '17 at 04:21

Rishi · Answer 1 · 2017-10-26T05:40:13.663

1

I don't see any reason why you should be printing the contents of the vector with the same index variable which is looping around the even numbers that you are adding. Perhaps, you should structure your code this way :

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> vect_name;
    //push to vector
    for (int i=10; i<21; i=i+2) {
        vect_name.push_back(i);
    }

    // print the contents of vector
    for (size_t i =0; i < vect_name.size(); ++i) {
        cout << vect_name[i] << " ";
    }
    cout << '\n';

    return 0;    
}

edited Oct 26 '17 at 05:40

answered Oct 26 '17 at 04:45

Rishi

1,387
10
14

Please don't encourage omitting braces around loop bodies. https://stackoverflow.com/questions/359732/why-is-it-considered-a-bad-practice-to-omit-curly-braces?lq=1 – Barmar Oct 26 '17 at 05:10

Saram Ali Azhar · Answer 2 · 2017-10-26T05:14:56.237

0

This is because you are missing a brace of the for loop. The looping variable you created in the for loop has a scope limited to it's braces, since you are missing the braces it takes just the next line only.

Because of that the loop variable i is not available

 int main()
{
vector<int> vect_name;
for (int i=10; i<21; i=i+2)
   vect_name.push_back(i);


for(int i=0; i<vect_name.size(); i++)
   cout << vect_name[i] <<endl;

return 0;

}

This should fix it.

edited Oct 26 '17 at 05:14

answered Oct 26 '17 at 04:19

Saram Ali Azhar

234
1
18

1

It's still wrong, since the indexes will be `0, 1, 2, ...`, but `i` is `10, 12, 14, ...` – Barmar Oct 26 '17 at 05:11
oops, I missed that! – Saram Ali Azhar Oct 26 '17 at 05:12
Well, using the iterator. it can be fixed. – Saram Ali Azhar Oct 26 '17 at 05:12
Now your answer is exactly the same as Rishi's. – Barmar Oct 26 '17 at 05:15

Shreevardhan · Answer 3 · 2017-10-26T05:35:34.587

You must be getting this error

error: ‘i’ was not declared in this scope
cout << vect_name[i] <<endl;
                  ^

Enclose the statements in parentheses to indicate loop body. Without the braces, only one following statement is taken as loop body.

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> vect_name;
    for (int i = 10; i < 21; i = i + 2) {
        vect_name.push_back(i);
        cout << vect_name[i] << endl;    // Will print zeroes
    }
    return 0;
}

However this will still give wrong results because arrays/vectors are 0 indexed in C++. You need to print in a separate loop.

A correct version of code will look like

#include <iostream>
#include <vector>
using namespace std;

int main() {
    vector<int> v(6, 10);
    for (int i = 0; i < v.size(); i++) {
        v[i] += (i * 2);
        cout << v[i] <<endl;
    }
    return 0;
}

Output

Error while adding elements to vector

3 Answers3