- Recall from
this webpage:
(
click here), that the
syntax to
declare a variable is:
extern dataType varName ;You can basically use this method to declare an array variable
- How
I usually
declare an
array variable:
- If the
array variables are:
int A[10]; float B[4][7]; // 2 dimensional array
I will declare the array variables by prepending the extern keyword as follows:
extern int A[10]; extern float B[4][7]; // 2 dimensional array
Example:
#include <stdio.h> extern int A[10]; // Declare array extern float B[4][7]; // Declare array int main(int argc, char *argv[] ) { int i, j; for (i = 0; i < 10; i++) A[i] = i; for (i = 0; i < 10; i++) printf("%d ", A[i]); printf("\n\n"); for (i = 0; i < 4; i++) for (j = 0; j < 7; j++) B[i][j] = i+j; for (i = 0; i < 4; i++) { for (j = 0; j < 7; j++) printf("%f ", B[i][j]); printf("\n"); } printf("\n\n"); } int A[10]; // Define array float B[4][7]; // Define array
- If the
array variables are:
- Example Program:
(Demo above code)
- Prog file: /home/cs255001/demo/C/Declare-array/declare-array1.c
How to run the program:
- To compile: gcc declare-array1.c
- To run: ./a.out
- Fact:
- The first dimension of an array declaration is optional !!!
In other words, you can declare array variables as follows:
#include <stdio.h> extern int A[ ]; // Declare array extern float B[ ][7]; // Declare array int main(int argc, char *argv[] ) { int i, j; for (i = 0; i < 10; i++) A[i] = i; for (i = 0; i < 10; i++) printf("%d ", A[i]); printf("\n\n"); for (i = 0; i < 4; i++) for (j = 0; j < 7; j++) B[i][j] = i+j; for (i = 0; i < 4; i++) { for (j = 0; j < 7; j++) printf("%f ", B[i][j]); printf("\n"); } printf("\n\n"); } int A[10]; // Define array float B[4][7]; // Define array
The reason for this is:
- The first dimension is
not needed to
find the
address (= location) of
an array element
(The first dimension is only used for array "out-of-bound" check.
Since C does not check array-out-bound errors, the first dimension is optional)