Pointers and Addresses in C

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Pointers and addresses play a crucial role in C programming. A pointer is a variable that holds the memory address of another variable. By utilizing pointers, you can directly access and manipulate memory addresses, making C a powerful and efficient programming language. This guide explores the concept of pointers, variables, addresses, pointer syntax, and dereferencing operators, providing insights into how they work in the context of C programming.

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Pointers COMP 11

Variables and Addresses int x; x = 42; 42 a x y char y; y = 'a';

Variables and Addresses int x; x = 42; 42 a x y 5678 1234 char y; y = 'a'; // & is the address of operator cout << "The address of x is "; cout << &x << endl; Variable address : where the variable is located in memory

What is a Pointer? A pointer is a variable that contains the address of a variable. --Inventors of C

What is a Pointer? A pointer is a variable that contains the address of a variable. --Inventors of C 42 a x y 5678 1234

What is a Pointer? A pointer is a variable that contains the address of a variable. --Inventors of C 42 a x p y 5678 7385 1234

What is a Pointer? A pointer is a variable that contains the address of a variable. --Inventors of C 1234 42 a x p y 5678 7385 1234

Pointer Syntax 9 42 int w = 9, x = 42; w x 9021 5678

Pointer Syntax 9 42 int w = 9, x = 42; int *p; /* "*p is an int" */ w x 9021 5678 ? p 1234

Pointer Syntax 9 42 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 9 42 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ cout << *p << endl; w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 9 42 int w = 9, x = 42; int *p; /* "*p is an int" */ w x 9021 5678 cout << *p << endl; ??? p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 9 42 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 42 42 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ w = *p; /* w now holds 42 */ w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 42 12 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ w = *p; /* w now holds 42 */ *p = 12;/* x now holds 12 */ w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Pointer Syntax 42 12 int w = 9, x = 42; int *p; /* "*p is an int" */ p = &x; /* p points to x */ w = *p; /* w now holds 42 */ *p = 12;/* x now holds 12 */ cout << *p + 1 << endl; w x 9021 5678 p 1234 When applied to a pointer, * is the dereferencing operator. If p is a pointer to location x, *p is the value at location x.

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x q

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 3 q

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 3 q

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 2 2, 2 q

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 2 2, 2 q

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 2 2, 2 q 2, 2

Check Your Understanding: Pointers What does this code print out? int x; int *p; int *q; x = 3; p = &x; cout << *p << , << x << endl; *p = *p - 1; cout << *p << , << x << endl; q = p; cout << *p << , << *q << endl; *q = *p - 1; cout << *p << , << *q << , << x << endl; p x 3, 3 1 2, 2 q 2, 2 1, 1, 1

Whats the point? void swap(int x, int y) { int temp; temp = y; y = x; x = temp; } int main() { int a = 7, b = 14; cout << a << << b << endl; // This should print 7 14 swap(a, b); cout << a << << b << endl; // This should print 14 7 }

Whats the point? x void swap(int *x, int *y) { int temp; temp = *y; *y = *x; *x = temp; } a3b5 y ff24 14 temp 9e2a int main() { int a = 7, b = 14; cout << a << << b << endl; swap(&a, &b); cout << a << << b << endl; } 7 14 a 1234 b 5678

Whats the point? x void swap(int *x, int *y) { int temp; temp = *y; *y = *x; *x = temp; } a3b5 y ff24 14 temp 9e2a int main() { int a = 7, b = 14; cout << a << << b << endl; swap(&a, &b); cout << a << << b << endl; } 7 7 a 1234 b 5678

Whats the point? x void swap(int *x, int *y) { int temp; temp = *y; *y = *x; *x = temp; } a3b5 y ff24 14 temp 9e2a int main() { int a = 7, b = 14; cout << a << << b << endl; swap(&a, &b); cout << a << << b << endl; } 14 7 a 1234 b 5678

Whats the point? void swap(int *x, int *y) { int temp; temp = *y; *y = *x; *x = temp; } Pointers enable pass-by-reference: A function can modify variables outside its scope via pointers to those variables. int main() { int a = 7, b = 14; cout << a << << b << endl; swap(&a, &b); cout << a << << b << endl; }

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } num1 num2

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } n x 4 num1 4 num2 10

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } n x 4 num1 4 num2 10

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } n x 4 num1 4 num2 1

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 2 4 num1 4 num2 1

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 2 4 num1 4 num2 2

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 3 4 num1 4 num2 2

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 3 4 num1 4 num2 6

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 4 4 num1 4 num2 6

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } i n x 4 4 num1 4 num2 24

Exercise: Pointers and Functions What does this code print out? void f(int n, int *x) { *x = 1; for (int i = 2; i <= n; i++) { *x = (*x) * i; } } int main() { int num1 = 4; int num2 = 10; f(num1, &num2); cout << num1 << << num2 << endl; return 0; } num1 4 num2 24

Pointers, Arrays, and Pointer Arithmetic arr: int arr[5]; arr[0] arr[1] arr[4]

Pointers, Arrays, and Pointer Arithmetic arr: int arr[5]; int *p = &arr[0]; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: int arr[5]; int *p = &arr[0]; arr[0] arr[1] arr[4] p: p+1: p+4: Given a pointer p that points to array element a[n], the expression p + i is a pointer to a[n + i].

Pointers, Arrays, and Pointer Arithmetic arr: 12 int arr[5]; int *p = &arr[0]; *(p + 1) = 12; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: 12 int arr[5]; int *p = &arr[0]; *(p + 1) = 12; p = p + 1; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: 12 int arr[5]; int *p = arr; //arr == &arr[0] *(p + 1) = 12; p = p + 1; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: 12 10 int arr[5]; int *p = arr; *(p + 1) = 12; p = p + 1; arr[3] = 10; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: 12 10 int arr[5]; int *p = arr; *(p + 1) = 12; p = p + 1; *(arr + 3) = 10; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic arr: 12 10 int arr[5]; int *p = arr; p[1] = 12; p = p + 1; *(arr + 3) = 10; arr[0] arr[1] arr[4] p:

Pointers, Arrays, and Pointer Arithmetic If arr is an array, then arr[i] is equivalent to *(arr + i). If p is a pointer, then *(p + i) is equivalent to p[i]. If arr is an array, then writing arr is equivalent to writing &arr[0]. In other words, the name of an array is a synonym for the address of the zeroth element of the array.