Easy tutorial for C / C ++ - Arrays 3 (Passing an array as an argument)

Easy tutorial for C / C ++ - Arrays 3 (Passing an array as an argument)

- When you use arguments to a function, you need to create as many arguments as needed. So what if you have a large number of arguments? It is easier to write a program by passing the name of the array as an argument to the function. 

- We have reviewed earlier that the name of the array is the address of the first element in the array. Let's take a look at the use of array names as arguments to functions. Let's look at an example.

Example Code

#include <iostream>

using namespace std;

void check(int*);

int main() {

     int arr[100] ;

     for(int i = 0; i < 100; i++){

             arr[i] = i ;

          }

     check(arr);

     return 0;

}

void check(int *p){

    cout<< "arr[5] = "<<p[5]<< endl;

    cout<< "arr[30] = "<<p[30]<< endl;

}

- Declare a function 'check' to check the element value of the passed array. We declared it as 'int *' because the argument to be passed is a pointer variable.

- Declared array 'arr' with 100 elements in main function. We then assigned values to each element through a for loop. The first value is 0 (arr [0] = 0) and the last value is 99 (arr [99] = 9).

- The 'check' function with argument which is a pointer variable is called. I used the array name 'arr' that I defined before as an argument. This is because the name of the array is a pointer variable that points to the address of the first element in the array.

- In the definition part of 'check', you can see the argument called int * p. Here, the name p is a pointer variable that I set arbitrarily. This 'p' is used within the 'check' function and represents the array 'arr' of the main function. The 'p' passed in can be used like an array. To test, we will print p [5] and p [30].

results :

arr[5] = 5

arr[30] = 30

- Notice that the value of the element stored in the array 'arr' is output. (arr [5] = p [5], arr [30] = p [30]) As a result, we have written a program that passes the array name as a parameter.

Pointer operation :

- You can apply arithmetic operators to pointers to access other values.

- If you put a '*' in front of a pointer variable, it means that it is the value stored in the address pointed to by the address value.

- Using the '+' operator shows the value stored in the place indicated by next address value. '-' indicates the value stored in the place indicated by the previous address value.

- We will revise the 'check' function definition in the previous example.

void check(int *p){

    cout<< "*p     = "<<*p << endl;

    cout<< "p[0]   = "<<p[0] << endl;

    cout<< endl;

    cout<< "*(p+2) = "<<*(p+2) << endl;

    cout<< "p[2]   = "<<p[2] << endl;

}

*p : You can get the first element value of an array by prepending '*' to the pointer variable 'p'. To see this, let's compare the output of 'p [0]'.

*(p+2) : From the first element of the array, you can get the value that the address of the element the next to the next is pointing to. Let's compare 'p [2]'.

results :

*p     = 0

p[0]   = 0

*(p+2) = 2

p[2]   = 2

- You can see that the result of using the index of the array and the result of performing the pointer operation are the same.