C programming declare global array

DataType var[ size ]; // One dimensional array DataType var[ size1 ][ size2 ]; // Two dimensional array

double a[10]; // array of 10 double variables

a[0] is located at the base address (in the example, we assume that the base address is 5000 )
a[1] is located at address base-address + 8 (a double variable occupies 8 bytes of memory)

Declaring a variable = Provide sufficient information to the C compiler to access the variable in memory.

Syntax to declare

extern DataTyp arrayVarName [ ] ;

File where the array is defined Declaring the (global) array variable double a[10]; // Array definition void func( ); // Declare func( ) int main( int argc, char* argv[] ) extern double a[ ]; // Array declaration void func( )

The main Prog file: click here
The array declaration Prog file: click here

How to run the program:

Suppose the C

extern double a[ ] ;

The C compiler will handle accessing the array element a[i] as follows:

It generate a dummy base address X (that the linker must update)

The C compiler will ignore any text between the brackets [. ] in an array declaration :

extern DataType arrayVarName [ /* ignored ! */ ] ;

DataType arrayVarName [ size1 ] [ size2 ] ;

Example: (array definition )

double a[3][5];

extern DataType arrayVarName [ ] [ size2 ] ;

File where the array is defined Declaring the 2-dim. array variable double a[3][5]; // Array definition void func( ); // Declare func( ) int main( int argc, char* argv[] )

extern double a[ ][5]; // Array declaration void func( ) < int i; for ( i = 0; i < 3; i++ ) < for ( j = 0; j < 5; j++ ) printf("a[%d][%d] = %lf ", i, j, a[i][j]); putchar('\n"); >>

The main Prog file: click here
The array declaration Prog file: click here

How to run the program:

The C compiler stores a 2-dimensional array in a row -wise fashion inside the computer memory

Example: double a[3][5] is stored in memory as follows:

As you can see from the above figure:

address of a[i][j] = base-address + ( i*SIZE-of-the-2nd-dimension + j ) * 8

The C compiler will ignore any text between the brackets [. ] in the leading (first) dimenison of an array declaration :

extern DataType arrayVarName [ /* ignored ! */ ] [ SIZE ] ;

File where the array is defined Declaring the 2-dim. array variable double a[3][5]; // Array definition void func( ); // Declare func( ) int main( int argc, char* argv[] )

extern double a[3][5]; // Array declaration void func( ) < int i; for ( i = 0; i < 3; i++ ) < for ( j = 0; j < 5; j++ ) printf("a[%d][%d] = %lf ", i, j, a[i][j]); putchar('\n"); >>