In this tutorial, we will learn about passing arrays to functions in C programming.

Like other values of variables, arrays can be passed to a function. Let us see how to pass an entire array to a function. Both one-dimensional arrays and multidimensional arrays can be passed as function arguments.

Passing one-dimensional array to the function

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While passing one-dimensional array to the function name of the array is passed as actual arguments and array variable with subscript is passed as formal arguments.

Ways of passing arrays as formal arguments.

1: Passing formal parameter as pointer

void func_name( int *name )
 {
     .......
 }

2: Passing formal parameters as sized array

void func_name( int name[10] )
 {
     .......
 }

3: Passing formal parameters as unsized array

void func_name( int name[] )
 {
     .......
 }

Example: C program to pass an array to the function that contains marks obtained by the student. Then display the total marks obtained by the student

#include <stdio.h>
int total_marks(int a[]); 
int main()
{
   int total = 0, marks[]={40,80,75,90,88}; 
   printf("Total marks = %d",total_marks(marks));
   return 0; 
} 
int total_marks(int a[])
{
   int sum=0,i;
   for (i=0;i<5;i++)
       sum=sum+a[i];
   return sum;
}  

Output

Total marks = 373

Explanation:
Here, the total_marks( ) function is used to calculate total marks. The for loop is used to access the array elements.

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Passing Multidimensional array to the function

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Like simple arrays, multidimensional arrays can be passed to the function. Two-dimensional array is indicated by two sets of brackets with array variable. The size of second dimension must be specified.

Example: C program to display the 3*3 matrix of given elements.

#include <stdio.h>
void matrix( int m[][3] )
{
   int i,j;
   printf("Matrix is :\n");
   for ( i=0;i<3;i++ )
   {
      for ( j=0;j<3;j++)
      {
         printf("%d",m[i][j]);
       }
      printf("\n");
   }
}
int main()
{
   int m[3][3] = {1,2,3,4,5,6,7,8,9};
   matrix(m);
   return 0;
}

Output

Matrix is :
1 2 3 
4 5 6
7 8 9

Note: It is a good idea to pass arrays by reference rather than value for performance reason. In the case of large arrays, passing by value will consume higher storage.

Difference between passing an entire array and individual array elements to a function.

#include <stdio.h>
#define SIZE 5

void changeArray( int x[], int s);
void changeElement( int y );

int main ()
{
    int arr[SIZE] = {0, 1, 2, 3, 4};
    int i;   //counter
    printf("passing entire array by reference.\n");
    printf("values of original array:\n");
    for(i = 0; i < SIZE; i++)
    {
        printf("%3d", arr[i]);
    }
    changeArray(arr, SIZE);   //passing array by reference
    printf("\nvalues of changed array:\n");
    for(i = 0; i < SIZE; i++)
    {
        printf("%3d", arr[i]);
    }
    printf("\nlet's see the value by passing array element\n"
           "\nvalue of arr[3] = %d", arr[3]);
    changeElement(arr[3]);  //passing array element arr[3] by value

    printf("\nvalue of arr[3] = %d", arr[3]);

}

void changeArray(int x[], int s)
{
    int j;    //counter variable
    for (j = 0; j<= SIZE; j++)
    {
        x[j] = x[j] * 2;
    }
}

void changeElement( int y)
{
   y = y * 2;    //multiplying array element by 2
   printf("\nvalue of 3rd element in changeElement = %d ", y);
}

Output

passing entire array by reference.
values of original array:
  0  1  2  3  4
values of changed array:
  0  2  4  6  8
let's see the value by passing array element

value of arr[3] = 6
value of 3rd element in changeElement = 12
value of arr[3] = 6

Explanation
In the above program, we can see the difference between passing an array by reference and element by value.

The program first prints the value of array and it is passed to changeArray() function, where elements are multiplied by 2. The modified result is printed.

In the second part, the program first prints the third element of modified array. After this third element of an array is passed to changeElement() function by value, where it is multiplied by 2 and value is printed.

Finally, in the main function the value of third element of an array is printed again but the value remains same.

Note: We can use const (constant) type qualifier to prevent modification of array elements in a function.

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