Overview
Welcome to Week 9 of C programming! This week, we will explore pointer. By the end of this tutorial, you will:
- Understand the basic concept of pointer
- Understand the difference between pointer to an array and pointer array (배열 포인터 vs 포인터 배열)
- Understand the double pointer
- Understand call-by-reference
Time Breakdown
- Introduction to a pointer
- Pointer to an array, and Pointer array
- double pointer
- call by reference
- Exercises & Q/A
**1. Pointer **
Pointer is a variable that stores the “memory address”.
*: Dereference operator
&: Address-of operator
%p: Format specifier for printing adresses
Example: How to define and use a Pointer
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| int a = 10;
int *p = &a;
printf("value of a: %d\n", a);
printf("address of a: %p\n", &a);
printf("value of p: %p\n", p);
printf("value of *p: %d\n", *p);
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Example Output:
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| value of a: 10
address of a: 0x7ffee45c489c
value of p: 0x7ffee45c489c
value of *p: 10
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**2. Pointer to an array vs Pointer array **
Pointer to an array (배열 포인터) : It is a singular pointer that points to a certain type of “array”.
-It is usually used when the parameter is 2-dimensional array.
Pointer array (포인터 배열) : An array that holds pointers as its elements.
Example: Pointer to an array vs Pointer array
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| #include <stdio.h>
int main() {
// Pointer to an array
char arr[3][7] = { "ABC", "DEF", "Point"};
char (*data1)[7] = arr; // 7개의 char로 이루어진 배열의 주소를 저장
for (int i = 0; i < 3; i++) {
printf("data1[%d]: %s\n", i, *(data1+i));
}
printf("===========================\n");
// Pointer array
char *data2[]={"ABC123456", "DEF", "Point"};
for (int i = 0; i < 3; i++) {
printf("data2[%d]: %s\n", i, data2[i]);
}
return 0;
}
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Pointer to an array
Pointer Array
Example Output:
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| data1[0]: ABC
data1[1]: DEF
data1[2]: Point
===========================
data2[0]: ABC123456
data2[1]: DEF
data2[2]: Point
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**3. Double Pointer **
Double pointer is a variable that stores the “memory address of pointer”.
Example: calculate the sum from 0 to n
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| void modify(int **double_ptr) {
**double_ptr = 999;
}
int main() {
int x = 10;
int *p = &x;
modify(&p);
printf("value of x: %d\n", x);
}
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Example Output:
**4. Call by reference **
Pointers allow modifying variables outside the function.
Example: How to define and use a Pointer
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| #include <stdio.h>
void swap(int *x, int *y) {
int temp = *x;
*x = *y;
*y = temp;
}
int main(void) {
int a = 5, b = 10;
swap(&a, &b);
printf("After swapping: a = %d, b = %d\n", a, b);
return 0;
}
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Example Output:
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| After swapping: a = 10, b = 5
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**Exercise 1: change multiple values in a function using pointers. **
- Initialize 4 int variables.
- Write a function that adds 1 to each variable.
- print the result
**Example Output **
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| =====before change=====
a = 1, b = 2, c = 3, d = 4
=====after change=====
a = 2, b = 3, c = 4, d = 5
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**Exercise 2: Find Maximum Value Using Pointers **
Write a program to find the maximum value in an array using pointers.
You can initialize the array in the way you want:
Eg.) int array[6] ={3, 2, 4, 22, 15, 6, 8};
**Example Output **
**Exercise 3: Find an Alphabet in a word **
- Please get an alphabet from a user.
- Please get a word from a user.
- Check if the word includes the alphabet ‘using pointer’. (Please find it using pointer arithmetic, not array index access.)
- Print if the alphabet is found.
**Example Output **
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| Please input the alphabet you want: i
Please input the word you want: apple
cannot find i!
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| Please input the alphabet you want: a
Please input the word you want: grammer
found a!
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