# Pointer

## Lecture PPT

### For Numerical Programming

{% file src="/files/oe4RqFkq6Cin9zBFFJi2" %}

### For Embedded Controller

{% file src="/files/RyEIPCEH9BHaeXvhq2Di" %}

## Summary

**코딩도장 요약** : [포인터 사용하기 핵심요약](https://dojang.io/mod/page/view.php?id=605)

What are Pointers?

A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location.

(a) Define a pointer variable: int \*ptr;

(b) Assign the address of a variable to a pointer: ptr = \&var;

(c) Access the value at the address available in the pointer variable: int value = \*ptr

![](/files/-MiW-t-Yab2248Ff6kUV)

#### For 32-Bit Word system (e.g. MCU)

32-CPU: 1 word = 4 bytes (32bit)

* Memory: byte units
* Int : 4 byte
* Pointer variable: 4 byte (default)

![TCP school.com](/files/-MiW-WuadRjqB08or-Fl)

![](/files/-MiW1AoykIxILMxHIjhc)

![](/files/-MiW1X3nPG3z30L6dzyg)

### Example Code

```cpp
#include <stdio.h>
#include <stdlib.h>

int main() {
int  var = 20;   
double a[4] = { 2, 2, 3, 4 };

// Pointer Declaration
int  *ptr;
double *ptr2 = NULL;// good practice for not Addr. assgined pointer
double *ptr3 = NULL;

// Pointer Assignment
ptr = &var;// store address of var in pointer variable
ptr2 = a;
ptr3 = &a[0];

printf("Address of var: %x\n", &var);
printf("Address of a  : %x\n", &a);
printf("Address of a[0]: %x\n", &a[0]);

// Using Pointer - Access the values pointed by Ptr
printf("\nAddress stored in \n  ptr: %x \n ptr2: %x  \n ptr3: %x\n", ptr, ptr2, ptr3);
printf("Value of \n  *ptr: %d \n *ptr2: %.1f  \n *ptr3: %.1f\n", *ptr, *ptr2, *ptr3);

system("pause");
return 0;
}
```

![](/files/-MiW069SJw0U_BA7RlLy)

## Exercise

* [Online C Compiler](https://www.onlinegdb.com/online_c_compiler)
* [Exercise Code](https://github.com/ykkimhgu/Tutorial-C-Program/tree/main/pointer-array)

### Exercise 1

다음 소스 코드를 완성하여 10과 20이 각 줄에 출력되게 만드세요.

```c
#include <stdio.h>

int main()
{
    int *numPtr;
    int num1 = 10;
    int num2 = 20;

    ① ________________
    printf("%d\n", *numPtr);

    ②_________________
    printf("%d\n", *numPtr);

    return 0;
}
```

실행 결과

```
10
20
```

<details>

<summary><strong>Solution</strong></summary>

```c
① numPtr = &num1;
② numPtr = &num2;
```

</details>

### Exercise 2

```c
int x =10;            
double y=2.5;
int *ptrX = &x;      
int *ptrY = &y;

/*
-Print the address of variable ‘x’
-Print the address of variable ‘y’
-Print the value of pointer ‘ptrX ‘
-Print the address of pointer ‘ptrX ‘
-Print the size of pointer ‘ptrX ‘
*/

/*
-Print the value of pointer ‘ptrY ‘
-Print the address of pointer ‘ptrY ‘
-Print the size of pointer ‘ptrY 
*/


```

### Exercise 3 - for EC only

```c
int x =10;            
double y=2.5;
int *ptrX = &x;      
int *ptrY = &y;


// Typecast pointer 'ptrY' to as (double *)

```


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