1. ECE 103 Engineering Programming Chapter 32 Array Parameters
Herbert G. Mayer, PSU CS
Status 6/4/2014
Initial content copied verbatim from
ECE 103 material developed by
Professor Phillip PSU ECE

2. Syllabus
1D Array Parameters
Multi-D Array Parameters
Examples

3. Passing Arrays to Functions (1-D)
Parameter list declaration:
dtype fun_name (dtype array_name[size]) {
/* Function body */ }
In the parameter list, specifying the 1-D array’s size is optional (the brackets are still required).
When passing an array to a function, use just the array name as the argument to the function. Do not pass the brackets! (pass M, not M[]) 2

4. Example:
#include <stdio.h> #define SIZE 3 int myfun (int c, int P[SIZE], int Q[]); int main (void) { int M[SIZE] = {12, 32, -5}; int Q[] = {1, 3, 4}; printf("%d\n", myfun(127, M, Q)); return 0; } int myfun (int c, int P[SIZE], int Q[]) {
return P[0]*Q[2] + P[1]*Q[1] + P[2]*Q[0] + c; } 3

5. Only the memory address of the array is passed to the function.
Pass-by-value: A passed array address that is stored in a function parameter is only a local copy.
The address value cannot be permanently altered.
However, the contents of the array at that address can be permanently changed!
If the values of a passed array should never be changeable, then use a const modifier.
If a function needs to know the number of elements in a passed array, that number must also be passed as a separate argument. 4

6. Example:
#include <stdio.h> #define SIZE 100 void printarray (int P[], int NumValidElements); int main (void) { int M[SIZE], value, k = 0; while (k < SIZE)
{ scanf("%d", &value);
if (value < 0) break;
M[k++] = value; }
printarray(M, k); return 0; } void printarray (int P[], int NumValidElements) {
int k;
for (k = 0; k < NumValidElements; k++)
printf("%d ", P[k]);
printf("\n"); 5

7. Example: #include <stdio.h> #define SIZE 10
/* Declare P to be a normal changeable array */
/* Declare Q to be a constant unchangeable array */ void fun (int P[], const int Q[], int ArySize);
int main (void) { int M[SIZE] = {0}, N[SIZE] = {0};
fun(M, N, SIZE);
return 0; }
void fun (int P[], const int Q[], int ArySize) {
P[0] = 99; /* This is allowed */
Q[0] = 99; /* ERROR: Compiler will complain */ } 6

8. Example: Actual output: y=99 : x=1 2 y=99 : x=1024 4096
#include <stdio.h>
void fun(int y, int x[]) {
y = 42;
x[0] = 1024; x[1] = 4096; }
int main (void)
int y = 99;
int x[] = {1, 2};
printf("y=%d : x=%d %d\n", y, x[0], x[1]);
fun(y, x);
return 0;
Actual output:
y=99 : x=1 2
y=99 : x= 7

9. Passing Arrays to Functions (Multi-Dimensional)
Parameter list declaration:
dtype fun_name (dtype array_name[size1][size2]…[sizeN]) {
/* Function body */ }
Specifying size1 is optional (the brackets are still required). The remaining sizes must be specified.
When passing an array to a function, use just the array name as the argument to the function. Do not pass the brackets! (pass M, not M[][]) 8

10. Example: #include <stdio.h>
void myfun (int P[7][3][2], int Q[][2][3]);
int main (void) {
int M[7][3][2] = {{{0}}};
int N[2][2][3] = {{{0}}};
myfun(M, N);
return 0; }
void myfun (int P[7][3][2], int Q[][2][3])
/* Function body */ 9