Problem Solving and Program Design in C (5th Edition) by Jeri R. Hanly and Elliot B. Koffman Chapter 6 (Pointers) © CPCS

CHAPTER 6 - Pointers # Chapter 61. Pointer 1a. Reference Operator 1b. Dereference Operator 1c. Declaring Variables 1. Pointer Illustration 2. Pointers and Functions 3. Ordering Three Numbers  column shows the topics index.  column shows the programs index.

Pointer A. Introduction  Pointers create dynamic data structures  data structures built up from blocks of memory allocated from the heap at run-time  Pointers handle variable parameters passed to functions  Pointers provide an alternative way to access information stored in arrays (Note: you will learn about arrays in the next chapter) B. Subtopics  Reference Operator (&)  Dereference Operator (*)  Declaring Pointers 1

Pointer - Reference Operator (&) A. Introduction  The memory can be imagined as a succession of memory cells  As soon as we declare a variable, the amount of memory needed is assigned for it at a specific location in memory (its memory address)  The address that locates a variable within memory is what we call a reference to that variable  reference to a variable can be obtained by preceding (&), known as reference operator  The variable that stores the reference to another variable is what we call a pointer 1a

Pointer - Reference Operator (&) B. Example 1a andy = 25; fred = andy; ted = &andy; 1.we have assigned the value 25 to andy (a variable whose address in memory is 1776). 2.copied the content of andy to fred. 3.copies the reference of andy to ted.

Pointer - Dereference Operator (*) A. Introduction  Using a pointer we can directly access the value stored in the variable which it points to. To do this, we simply have to precede the pointer's identifier with an asterisk (*), which acts as dereference operator  can be literally translated to "value pointed by". B. Example 1b andy = 25; ted = &andy; beth = *ted; *(&andy) == andy

Pointer - Declaring Variables A. Introduction  Due to the ability of a pointer to directly refer to the value that it points to, it becomes necessary to specify in its declaration which data type a pointer is going point to B. Syntax C. Example  int *number;  char *character;  float *greatnumber; 1c

Pointer C. Conclusion  Notice the difference between the reference and dereference operators:  & is the reference operator and can be read as "address of“  * is the dereference operator and can be read as "value pointed by" 1c andy = 25; ted = &andy; beth = *ted; *(&andy) == andy 1

Implementation Problem Analysis Design Outline Testing Maintenance Pointer Illustration P1 #include int main (void) { int firstvalue, secondvalue; int *mypointer; mypointer = &firstvalue; *mypointer = 10; mypointer = &secondvalue; *mypointer = 20; printf("firstvalue is %d\n", firstvalue); printf("secondvalue is %d\n", secondvalue); return 0; }

Implementation Problem Analysis Design Outline Testing Maintenance Pointers and Functions P2 #include void calculation( int num, /* input */ int *cal1, /* output */ int *cal2) /* output */ { *cal1 = num + num; *cal2 = num * num; } int main(void) { int value; /* input: number entered by user */ int sum; /* output: num + num */ int multi; /* output: num * num */ printf("Enter a value to analyze> "); scanf("%d", &value); calculation(value, &sum, &multi); printf("Sum = %d, Multiply = %d\n", sum, multi); return(0); }

Implementation Problem Analysis Design Outline Testing Maintenance Ordering Three Numbers P3

Implementation Problem Analysis Design Outline Testing Maintenance Ordering Three Numbers P3