c++ passing function into main error

Question

hi i have following c++ code where i want call function into main, following are my code:

#include <iostream>
#include <numeric>

int main()
{

    using namespace std;

    readData();

    int sumA = accumulate(A, A + sizeof(A) / sizeof(int), 0);
    int sumB = accumulate(B, B + sizeof(B) / sizeof(int), 0);

    cout << ((sumA > sumB) ? "Array A Greater Than Array B\n" : "Array B Greater Than Array A\n");


    return 0;
}

void readData()
{

int A[] = { 1, 1, 8};
int B[] = { 2, 2, 2};
}

I have following error on cli :

test.cpp:3:7: error: storage size of ‘B’ isn’t known
test.cpp:4:7: error: storage size of ‘A’ isn’t known

Where am i wrong here? Thanks

'`cout << ((sumA > sumB) ? "Array A Greater Than Array B\n" : "Array B Greater Than Array A\n");`'? What about the case where `sumA == sumB`? — johnsyweb, Mar 05 '13 at 13:33
how can i compare sums of elements in array..? for above situation how can we writte in better way — d3bug3r, Mar 05 '13 at 13:40
Complete lack of understanding of how language works. Get a good book. — , Mar 05 '13 at 14:15
Your compiler should emit some more useful errors (such as those here: http://liveworkspace.org/code/2g3oE0$0) but I'd expect anyone with a modicum of [tag:c++] experience to be able to work it out from the errors you gave there. `A` and `B` are not declared in `main()` and therefore cannot be used in that context. You need to rewrite this code to make more sense in your chosen programming language. — johnsyweb, Mar 05 '13 at 14:32

score 6 · Answer 1 · answered Mar 05 '13 at 13:30

6

The variables A and B are local to the function readData and not accessible from any other function.

Either declare them as global variables (not recommended) or as local variables in main and pass them as arguments to the readData function.

I also recommend you use std::vector instead of plain arrays.

answered Mar 05 '13 at 13:30

Some programmer dude

400,186
35
402
621

1

The use of plain arrays will make more sense if you read this: http://stackoverflow.com/a/15197954/78845 – johnsyweb Mar 05 '13 at 13:32
how to write it more better..? any ideas – d3bug3r Mar 05 '13 at 13:41

score 0 · Answer 2 · edited Dec 16 '13 at 10:44

0

First of all, be careful with taking the size of arrays in C and C++. Read here for more information: http://www.cplusplus.com/faq/sequences/arrays/sizeof-array/

However do use std::vector instead like this.

#include <iostream>
#include <vector>
#include <numeric>

typedef std::vector<int> int_vec_t;

//Call by reference to set variables in function
void readData(int_vec_t& v1, int_vec_t& v2)
{
  v1 = int_vec_t{1,1,8}; //This only works for C++11
  v2 = int_vec_t{2,2,2};
}

void readUserData(int_vec_t& v)
{
  for(;;)
  {
    int val;
    std::cin>>val;
    if(val == 0) break;
    v.push_back(val);
  }
}

int main()
{
    using namespace std;

    int_vec_t A;
    int_vec_t B;

    readData(A,B);
    //Or
    readUserData(A);
    readUserData(B);

    int sumA = accumulate(A.begin(), A.end(), 0); //Then use iterators
    int sumB = accumulate(B.begin(), B.end(), 0);

    cout << ((sumA > sumB) ? "Array A Greater Than Array B\n" : "Array B Greater Than Array A\n");

    return 0;
}

edited Dec 16 '13 at 10:44

BenMorel

34,448
50
182
322

answered Mar 05 '13 at 13:59

AxelOmega

974
10
18

how to pass user input to both of array then?lets says we want to pass 5 elements into each array.. – d3bug3r Mar 05 '13 at 14:07
something in the line of the `readUserData` function I just added. However handling user input is a tricky matter which is outside the scope of this answer. – AxelOmega Mar 05 '13 at 14:17
where is readUserData..? – d3bug3r Mar 05 '13 at 14:20
@AxelOmega not working, got errors.. – Saraswathi Apavoo Mar 05 '13 at 15:05

c++ passing function into main error

2 Answers2

Linked