Call By Address Parameters (Pointers)

1. Call By Address Parameters (Pointers) Chapter 5

2. Functions that “return” more than a single value • What if we need more than one value to be returned from a function? • For example, imagine we need a function to to calculate how many quarters, dimes, nickels and pennies should be given when making change. • Call by address parameters allow a function to “return” more than a single value • Rather than passing the value of a parameter to a function the address of a variable is passed to the function • Any changes made by the function are then made to the memory location of that variable

3. Declaration of a Pointer Variable • A pointer variable holds thememory address of another variable. • By convention, many programmers name a pointer variable with the same name as the variable "pointed" to, but starting with a p_ • A pointer variable is always declared to be the same type as the variable it points to and must have a * (an asterisk) in front of it, to identify it as a pointer.For example, to declare a pointer to point to an int variable named num, the declaration would be: int *p_num; /* pointer to int variable num */

4. Assignment of a Pointer Variable • To assignp_num the address of num (i.e. to "point" to num), use the following assignment statement: p_num = # • Translated, this means: p_num is assigned the value of the address of the variable num

5. Pointers Exercise • Write a function sort 2 that is passed 2 integer values and returns the values in ascending order as shown in main below: • void sort2(int n1, int n2, int *p_num1, int *p_num2); • main() • { int int1, int2, first, second; • printf(“Enter 2 integers: “); • scanf(“%d %d”, &int1, &int2); • sort2(int1, int2, &first, &second); • printf(“First: %d, Second: %d\n”,first, second); • }

6. Pointers Exercise Solution • void sort2(int n1, int n2, int *p_num1, int *p_num2){ • if (n1 <= n2) { • *p_num1 = n1; • *p_num2 = n2; • } else { • *p_num1 = n2; • *p_num2 = n1; • } • }

7. Pointer Exercise Write a function to calculate how many quarters, dimes, nickelsand pennies should be given when making change to be used in program shown below: void makechange(double, int *, int *, int *, int *); main() { double amount; int numqtrs, numdimes, numnickels, numpennies; printf("Amount of money (in dollars and cents): $"); scanf("%lf", &amount); makechange(amount, &numqtrs, &numdimes, &numnickels, &numpennies); printf(“Change: %d quarters,%d dimes,", numqtrs, numdimes); printf("%d nickels, %d pennies\n" , numnickels, numpennies); }