Initialization of a multidimensional arrays in C/C++

In C/C++, initialization of a multidimensional array can have left most dimensions as optional. Except for the leftmost dimension, all other dimensions must be specified.

For example, the following program fails in compilation because two dimensions are not specified.

C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
  int a[][][2] = { {{1, 2}, {3, 4}},
                   {{5, 6}, {7, 8}} };  // error
  cout << sizeof(a);
  getchar();
  return 0;
}

// This code is contributed by Mayank Tyagi

C

#include<stdio.h>
int main()
{
  int a[][][2] = { {{1, 2}, {3, 4}},
                   {{5, 6}, {7, 8}}
                 };  // error
  printf("%d", sizeof(a));
  getchar();
  return 0;
}

Output

./Solution.cpp: In function 'int main()':
./Solution.cpp:5:14: error: declaration of 'a' as multidimensional array must have bounds for all dimensions except the first
   int a[][][2] = { {{1, 2}, {3, 4}},
              ^
./Solution.cpp:7:18: error: 'a' was not declared in this scope
   cout << sizeof(a);
                  ^

Multidimensional Array can be initialized using an initializer list as shown:

Syntax

array_name[x][y] = { {a, b, c, ... }, ........., { m, n, o ...}};

Following 2 programs work without any error.

C++

// Program 1
#include<bits/stdc++.h>
using namespace std;
int main()
{
  int a[][2] = {{1, 2}, {3, 4}}; // Works
  cout << sizeof(a); // prints 4*sizeof(int)
  return 0;
}

// This code is contributed by Mayank Tyagi

C

// Program 1
#include<stdio.h>
int main()
{
  int a[][2] = {{1,2},{3,4}}; // Works
  printf("%lu", sizeof(a)); // prints 4*sizeof(int)
  getchar();
  return 0;
}

Output

16

C++

// Program 2
#include<bits/stdc++.h>
using namespace std;
int main()
{
  int a[][2][2] = { {{1, 2}, {3, 4}},
                     {{5, 6}, {7, 8}} }; // Works
  cout << sizeof(a); // prints 8*sizeof(int)
  return 0;
}

// This code is contributed by Mayank Tyagi

C

// Program 2
#include<stdio.h>
int main()
{
  int a[][2][2] = { {{1, 2}, {3, 4}},
                     {{5, 6}, {7, 8}}
                   }; // Works
  printf("%lu", sizeof(a)); // prints 8*sizeof(int)
  getchar();
  return 0;
}

Output

32

The below example is multidimensional array in  C/C++.

C++

#include <iostream>
using namespace std;

int main() {

    // code
    int a[2][3] = { { 1, 3, 2 }, { 6, 7, 8 } };
    int i, j;
    for (i = 0; i < 2; i++) {
        for (j = 0; j < 3; j++) {
            cout << "\n a[" << i << "][" << j << "]=" << a[i][j];
        }
    }
    return 0;
}

C

#include <stdio.h>

int main() {

    // code
  int a[2][3] = { { 1, 3, 2 }, { 6, 7, 8 } };
    int i, j;
    for (i = 0; i < 2; i++) {
        for (j = 0; j < 3; j++) {
            printf("\n a[%d][%d]=%d", i, j, a[i][j]);
        }
    }
    return 0;
}

Output

 a[0][0]=1
 a[0][1]=3
 a[0][2]=2
 a[1][0]=6
 a[1][1]=7
 a[1][2]=8

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