Pointer

Lecture PPT

Lesson

코딩도장 핵심요약: 포인터 사용하기 핵심요약

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

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

Example Code

#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;
}

Exercise

• Online C Compiler

• Exercise Code

• Exercise-Solution Code

Exercise 1

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

#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

Solution

① numPtr = &num1;
② numPtr = &num2;

Exercise 2

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 
*/

/* for Embedded Controller
- Typecast pointer 'ptrY' to as (double *)
*/

Solution

Exercise Solution File