Handling input into struct elements with array

Question

I'm doing an assignment that involves structs.

You are to make a struct with three variables and declare 3 instances of that struct. The program will then ask for the user to input 9 pieces of information. I don't like having to type cout and cin unnecessarily (9 sequential times?), so I was thinking I could use loops to handle the input, like I've done with arrays earlier. I tried it out, but have been unsuccessful so far. Am I on to something with this?

struct Randomstruct {
  int var1, var2, var3;
}

int main() {
  Randomstruct struct1, struct2, struct3;
  for(int i = 1; i<=3; i++) {
    for(int j = 1; j<=3; j++) {
      cout << "Enter data for var" << j << " in struct" << struct(i) << ": ";
      cin struct(i).var(i);
      }
    }
  }
}

I'm really wondering how I can make the struct(i).var(i) thing work. Is it even possible?

Answer 1

No

The struct(i).var(i) will not work.

You could make vectors/arrays but as you have written the task it sounds it's not allowed.

Example

struct Randomstruct {
    int var[3];
};

...and access with

struct1.var[i]

Answer 2

Just a sligh tweak to your syntax:

struct Randomstruct
{
    int var[3];  // Use an array to index things by integer.
}; // You forgot this semicoln

int main()
{
    Randomstruct struct[3];  // Again another array

    // Nearly all programming languages used 0 based arrays.
    // So loop from  0 -> (array size -1) ie use smaller than
    for(int i = 0; i<3; i++)
    {
       // Again user 0 based index.
       for(int j = 0; j<3; j++)
       {
           cout << "Enter data for var" << j << " in struct" << struct(i) << ": ";

           // Use the >> operator to get stuff from the stdin.
           // Arrays are indexed via the operator [<index>]
           cin >> struct[i].var[j];
       }
    }
}

Answer 3

You could do this, but it seems a little silly:

#include <iostream>

typedef struct _random_struct
{
    int var1;
    int var2;
    int var3;
} random_struct;

typedef struct _other_struct
{
    int var[3];
} other_struct;

union being_lazy
{
    random_struct r;
    other_struct o;
};


int main()
{
    random_struct st[3];
    being_lazy l[3];
    for(int i = 0; i < 3; ++i)
    {
        for(int j = 0; j < 3; ++j)
        {
            std::cout << "Enter data for var" << j << " in struct" << i << ": ";
            std::cin >> l[i].o.var[j];
        }
    }

    for(int i = 0; i < 3; ++i)
    {
        st[i] = l[i].r;
    }

    for(int i = 0; i < 3; i++)
    {
        std::cout << "struct" << i << ".var1 == " << st[i].var1 << std::endl;
        std::cout << "struct" << i << ".var2 == " << st[i].var2 << std::endl;
        std::cout << "struct" << i << ".var3 == " << st[i].var3 << std::endl;
    }
}

You'd need to make sure that both random_struct and other_struct have the same structure in memory, or bad things might happen.

Really though, if you accessing individual fields is too painful, you either want to just directly use arrays, or re-think your code.