Pointers and Output Parameters

1. Pointers and Output Parameters

2. Pointers • A pointer contains the address of another memory cell • i.e., it “points to” another variable double cost = 100.00; cost:1024 100.00 double *cost_ptr = &cost; cost_ptr:2048

3. Pointers • A pointer contains the address of another memory cell • i.e., it “points to” another variable double cost = 100.00; cost:1024 100.00 double *cost_ptr = &cost; cost_ptr:2048 1024

4. Pointers • A pointer contains the address of another memory cell • i.e., it “points to” another variable double cost = 100.00; printf(“cost: %lf”, cost); printf(“cost_ptr: %d”, cost_ptr); printf(“&cost: %d”, &cost); printf(“&cost_ptr: %d”, &cost_ptr); printf(“*cost_ptr: %lf”, *cost_ptr); cost:1024 100.00 double *cost_ptr = &cost; cost_ptr:2048 1024

5. Pointers • A pointer contains the address of another memory cell • i.e., it “points to” another variable double cost = 100.00; cost: 100.00 cost_ptr: 1024 &cost: 1024 &cost_ptr: 2048 *cost_ptr: 100.00 cost:1024 100.00 double *cost_ptr = &cost; cost_ptr:2048 1024

6. Call By Value int main(void) { int a = 5, b = 1; swap(a, b); printf(“a=%d, b=%d”, a, b); return (0); } void swap(int a, int b) { int tmp = a; a = b; b = tmp; printf(“a=%d, b=%d”, a, b); }

7. Call By Value int main(void) { int a = 5, b = 1; swap(a, b); printf(“a=%d, b=%d”, a, b); return (0); } void swap(int a, int b) { int tmp = a; a = b; b = tmp; printf(“a=%d, b=%d”, a, b); } Prints: a=1, b=5 a=5, b=1

8. Call By Value a:1036 5 b:1032 1 main a:1028 5 a:1028 1 b:1024 1 b:1024 5 swap

9. Call By Reference a:1036 5 b:1032 1 main a:1028 b:1024 swap

10. Call By Reference int main(void) { int a = 5, b = 1; swap(&a, &b); printf(“a=%d, b=%d”, a, b); return (0); } void swap(int *a, int *b) { int tmp = *a; //follow the pointer to a, get the value, and store it in tmp *a = *b; *b = tmp; printf(“a=%d, b=%d”, *a, *b); }

11. Call By Reference a:1036 1 b:1032 5 main a:1028 a:1028 b:1024 b:1024 swap

12. fraction.c • Create a single function that will multiply a fraction.