How To Pass Array to Function in C++.

As we know that an array is a collection same kind of data in a contiguous memory location but can we pass the array data as an argument to a function? The answer to this question is no. We cannot pass the entire array as an argument to a function but we can pass a pointer to an array. 

We have totally different methods for passing a one-dimensional and two-dimensional array to a function in C++. Let's discuss both of them one by one:

Passing One-Dimensional Array to Function.

We have passed the name of our array without an index to a function and the name of the array behaves like a pointer folding the address of the first element of the array. Any changes made in the array inside the function will directly affect the elements of the main array. 

C++ Example Code:

//C++ Example to show ways of Passing Array to Function
#include<iostream>
using namespace std;

//Formal parameter as unsized array
void funType1(int arr[], int n){

	int size = sizeof(arr)/sizeof(arr[0]);
	cout<<"\nSize of array inside fun1: "<<size<<endl;

	arr[2] = 10;  
	cout<<"Array Elements in fun1: ";
	for(int i = 0; i < n; i++)
	  cout<<arr[i]<<" ";
}

//Formal parameter as a pointer
void funType2(int *arr, int n){

	int size = sizeof(arr)/sizeof(arr[0]);
	cout<<"Size of array inside fun2: "<<size<<endl;

	arr[n-1] = 23; 
	cout<<"Array Elements in fun2: ";
	for(int i = 0; i < n; i++)
	  cout<<arr[i]<<" "; 
}

int main(){

	int arr[] = {3, 4, 5, 7, 8, 9};
	//size of array
	int n = sizeof(arr)/sizeof(arr[0]);
	cout<<"Size of given array: "<<n<<endl;

	cout<<"Array Elements: ";
	for(int i = 0; i < n; i++)
	  cout<<arr[i]<<" ";
        
        //function 1 call
	funType1(arr, n);
	cout<<endl;

        //function 2 call
	funType2(arr, n);

	return 0;
}

Output:

Size of given array: 6
Array Elements: 3 4 5 7 8 9
Size of array inside fun1: 2
Array Elements in fun1: 3 4 10 7 8 9
Size of array inside fun2: 2
Array Elements in fun2: 3 4 10 7 8 23

We have two ways of writing an array into a function as an argument, 

• The first is passing an unsized array as a parameter. (syntax: fun(int arr[])) 
• The second is passing as a pointer. (syntax: fun(int *arr))

Both hold the address of only the first element of the array.

We cannot calculate the size of the array inside the function we must have to pass the array size as a parameter. 

Passing Two-Dimensional Array to Function.

To pass a 2D array (also known as a matrix) to a function we must have to pass the second dimension value to the function were passing the first dimension value is totally optional. 

Syntax: fun(int arr[][m])

C++ Example Code:

//C++ Example code for passing 2D array to function
#include<iostream>
using namespace std;

//Passing matrix to a function
void fun2DArray(int arr[][3], int r, int c){
	cout<<"Elements of 2D Array: "<<endl;
	for(int i = 0; i < r; i++){
		for(int j = 0; j < c; j++){
			cout<<arr[i][j]<<" ";
		}
		cout<<endl;
	}
}
int main(){
	
	int arr[][3] = {{2, 3, 7},{9, 5, 1},{4, 6, 2}};
	
	int row = sizeof(arr)/sizeof(arr[0]);
	int col = sizeof(arr[0])/sizeof(arr[0][0]);

	fun2DArray(arr, row, col);

	return 0;
}

Output:

Elements of 2D Array: 
2 3 7
9 5 1
4 6 2

In the above code, you can also check how we can calculate the number of rows and columns of a 2D Array using the sizeof() operator.

Next:

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