CODEWITHSUNDEEP
c++visual-c++
user3093536
user3093536

Reputation: 95

Definition of variables into arrays and proper syntax

I have a code here:

#include <iostream>
#include <string>

using namespace std;
int main()
{
    int a, b=0,d,f=1;
    string c, e, g;

    cout<<":"<<endl;
    cin>>a;
    string question[a];
    for(;b<a;b++)
    {
        cout<<"#"<<b+1<<":"<<endl;
        getline(cin,c);
        question[b]=c;
        cout<<":"<<endl;
        cin>>d;
        getline(cin,e);
        question[b][d+1]{e};
        for(;f<d;f++)
        {
            cout<<" #"<<f<<":"<<endl;
            getline(cin,g);
            question[b][f]=g;
        }
    }
    system("pause");
    return 0;
}

This does not compile and I believe it is because the variables -that I want to define the first availabe spaces in arrays as- are seen as characters and not their values that would be defined by the user input. I'm trying to get my bearings on C++ right now; could somebody explain to me in simple terms why this does not work and how I should fix my problem?

Error:

Error   1   expected constant expression    12
Error   2   cannot allocate an array of constant size 0 12
Error   3   'question' : unknown size   12
Error   4   syntax error : missing ';' before '{'   21
Error   5   syntax error : missing ';' before '}'   21
Error   6   '=' : cannot convert from 'std::string' to 'char'   27
Error   7   IntelliSense: expression must have a constant value 12
Error   8   IntelliSense: expected a ';'    21  19

Upvotes: 0

Views: 51

Answers (3)

Paweł Stawarz
Paweł Stawarz

Reputation: 4012

This does not compile because you're trying to make an array's size dependant on the user input, and in c++ the array size needs to be already known at compile time. Change

string question[a];

to

string *question = new string[a];

and just before return 0 do:

delete [] question;

Also this line:

question[b][d+1]{e}

doesn't really have sense. The first index is gonna access element b of the array, the second one will access element d+1 of the string, and you're trying to do something with a string there. Strings are built of characters, not other strings. Same appplies to line 27.

Upvotes: 1

A.E. Drew
A.E. Drew

Reputation: 2137

The problem is likely your attempt to have an array of strings of size a when a is not known at compile time.

cout<<"Enter the number of questions:"<<endl;
cin>>a;
string question[a];         //Creates an array for questions

You could use a std::vector of strings instead of a c-style array. A std::vector allows for the size to change dynamically.

You could also allocate an array on strings on the heap, by using 

string* question_ptr = new string[a];

And then calling when done with the array:

delete[] question_ptr ;

Upvotes: 1

tabstop
tabstop

Reputation: 1761

C++ isn't big on variable-length arrays, so this

string question[a];

is going to be bad news. The usual C++ idiom for that sort of thing is a vector or (in C++11) an array.

Upvotes: 0

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