2-D Array — “Too many initializer values”警告/错误

Question

I'm new to programming. I tried looking at a bunch of similar questions to mine on here, but either they were too advanced for me to understand or didn't quite apply to/help me with my situation.

I just learned about 2-D arrays, so I am doing an assignment about them. (The assignment is about movie ratings, which will explain the names of the variables/arrays/etc in my code)

One of my functions is supposed to assign predetermined values to an integer array. However, in this function when I try to initialize the array/assign integers to it, I get one of those red squiggly lines which says "Too many initializer values" when I hover over it.

1. Why does this show up when there AREN'T too many values being put into the array? (see code below)

   I think I've seen in other posts/answers that you can't assign to an array--is this true/is this what's going wrong? If so, why? And how else might I put values into this array, if not by just doing something like array[x][y]={...}?

2. Have I used/passed the correct arguments/parameters into the function?

Here is some of my code (not my complete program, just the parts relevant to this question):

#include <iostream>
#include <cstdlib>

using namespace std;

//Global constants
const int NUM_REVIEWERS = 4;   //Number of rows in reviews array
const int NUM_MOVIES = 6;      //Number of columns in reviews array     

//function prototype
void initialRatings(int[][NUM_MOVIES]); 

int main()
{
    // Variable declarations
    int someArray[NUM_REVIEWERS][NUM_MOVIES];  // Ratings for reviewers
    int choice;

    initialRatings(someArray); //function call with actual argument passing in the array and the number of rows

    return 0;
}


/***************************************************************************
    function definition for initialRatings

    this function sets all data elements in the 2-D array to the sample data

****************************************************************************/

void initialRatings(int array[][NUM_MOVIES])
{
    array[NUM_REVIEWERS][NUM_MOVIES] = { {3, 1, 5, 2, 1, 5 }, 
                                         {4, 2, 1, 4, 2, 4 },//the beginning of this row is where I get the error 
                                         {3, 1, 2, 4, 4, 1 }, 
                                         {5, 1, 4, 2, 4, 2 } };
}

The exact errors I get when I try to compile it are:

error C2440: '=': cannot convert from 'initializer list' to 'int'

and

message : The initializer contains too many elements

I'm using Microsoft Visual Studio. I've tried using my book/looking it up, but I'm having a hard time finding the answer(s) I'm looking for. Feel free to correct anything I say incorrectly. I'm here to learn!

Answer 1

You can use initializer list only for initialization, and not for assignment. This means you'll have to assign values when you're initialising the array for the first time, ie,

int array[NUM_REVIEWERS][NUM_MOVIES] = 
      { {3, 1, 5, 2, 1, 5 }, 
      {4, 2, 1, 4, 2, 4 },
      {3, 1, 2, 4, 4, 1 }, 
      {5, 1, 4, 2, 4, 2 } };

Also, try to use another variable name, since array is a reserved word in C++ (although it is not a problem but it isn't a good coding practice).

Answer 2

the problem with your code is that you can only do the assignment bellow in the variable declaration, ie, you can only do multiple assignment of the array, when you declare the array.

array[NUM_REVIEWERS][NUM_MOVIES] = 
      { {3, 1, 5, 2, 1, 5 }, 
      {4, 2, 1, 4, 2, 4 },//the beginning of this row is where I get the error 
      {3, 1, 2, 4, 4, 1 }, 
      {5, 1, 4, 2, 4, 2 } };

In your case the variable array its already declared so the only way to assign values to the different indexes its by iterating or directly assigning a value to each position.

The assignment you're trying to do only works if it was something like this:

int array[NUM_REVIEWERS][NUM_MOVIES] = 
      { {3, 1, 5, 2, 1, 5 }, 
      {4, 2, 1, 4, 2, 4 },//the beginning of this row is where I get the error 
      {3, 1, 2, 4, 4, 1 }, 
      {5, 1, 4, 2, 4, 2 } };

In the variable declaration.

If you still want to use the void initialRatings(int array[][NUM_MOVIES]) function here is one alternative.

void initialRatings(int array[NUM_REVIEWERS][NUM_MOVIES])
{
    array[0][0] = 3;
    array[0][1] = 1;
    array[0][2] = 5;
    array[0][3] = 2;
    array[0][4] = 1;
    array[0][5] = 5;

    array[1][0] = 4;
    array[1][1] = 2;
    array[1][2] = 1;
    array[1][3] = 4;
    array[1][4] = 2;
    array[1][5] = 4;

//... Do the same for the other rows
}

And if you want to see the result after calling the initialRatings function print the values of each position to the console.

int main()
{
    // Variable declarations
    int someArray[NUM_REVIEWERS][NUM_MOVIES];  // Ratings for reviewers
    initialRatings(someArray); //function call with actual argument passing in the array and the number of rows
    for (int row = 0; row < NUM_REVIEWERS; row++)
    {
        for (int column = 0; column < NUM_MOVIES; column++)
        {
            cout << someArray[row][column] << " "; // print the array value and a space to separate 
                                                    // the values in each column
        }
        cout << endl; // add line break for each row
    } 
    return 0;
}

Answer 3

In C++, when you use arr[i][j] , you are actually accessing a single element of that array. Basically, arr[i][j] is actually *(*(arr+i) + j) . And * here is used to dereference a pointer.

Let's take a simpler example: suppose you have an array int a[3] = {4, 5, 6}; , there will be 3 memory "blocks" allocated to hold the values, each taking 4 bytes (suppose 1 int takes 4 bytes).

|   4    |   5       |   6        |
0x1      0x1 + 4     0x1 +8       0x1+12
arr      arr+1       arr+2        arr+3

For pointers, you can think them as some special variables which hold other variable's memory addresses. As the name pointer suggests, they are used to point to other variables.

In C/C++, array names are actually const pointers. And you can use arr+i to point to any one of the 3 blocks.

*(arr+i)

Adding a dereference mark * helps you to fetch the actual value stored in that block, eg *(arr+1) == 5 . What's more, arr[i] is actually another form of *(arr+i) .

So that's what happened behind when you write array assignment statements like arr[i] = 1 . Things get a bit complicated from 1d to 2d. But the genenal idea is the same: when you assign to arr[i][j] , you are writing values to one certain location of the 2d array.

And that's why you get the error error C2440: '=': cannot convert from 'initializer list' to 'int' .

As for initializer list , as the name suggests, it's used at initialzing time.