8.4. Operations on structures

Most of the operators we have been using on other types, like mathematical operators ( +, %, etc.) and comparison operators (==, >, etc.), do not work on structures by default. It is possible to define the meaning of these operators for the new type, but we won’t do that in this book.

A structure can be initialized with a braced list of member values:

struct point {
    double x, y;
};

point blank = {3.0, 4.0};

The members are initialized in declaration order: x receives 3.0 and y receives 4.0. Initialization creates an object; assignment replaces an existing object's value. In C++20, we can use a braced list in an assignment as well:

blank = {12.0, 3.2};

We can also copy one structure to another:

Example operations_structures_AC_1
 1#include <iostream>
 2
 3struct point {
 4    double x, y;
 5};
 6
 7int main() {
 8    point p1 = {3.0, 4.0};
 9    point p2 = p1;          // copy initialization
10    p1 = {12.0, 3.2};      // assignment from a braced list
11    p2 = p1;              // copy assignment
12    std::cout << p2.x << ", " << p2.y << '\n';
13}

The output is 12, 3.2. Copying or assigning a point copies the values of both members.

Q1

Click on all incorrect statements in C++20. Assume point is the structure defined above.


    
    
    
    
    
    
    
}

Q2

Construct a block of code that correctly initializes the instance variables of a structure.

  1.    double x, y;
};
  2. blank = 12.0; #distractor
  3. blank = { 12.0, 3.2 } #distractor
  4. blank = { 12.0, 3.2 };
  5. int blank; #distractor
  6. int main() {
  7. point blank;
  8. struct point {
  9. }

Q3

Which operators do NOT work on structures. Select all that apply.