Lab guide #6

1. Lab guide #6 C Pointers Review & Lab assignments

2. Key points • Pointers and pointer operators. • Pass arguments to functions by reference by using pointer. • sizeof Operator and Pointer Arithmetic. • The close relationships among pointers, arrays and strings. • Pointers to functions.

3. Pointers and pointer operators • Pointer: • Contains address of a variable that has a specific value (indirect reference) • Definitions: int *myPtr1, *myPtr2; • Operators: • Address operator: & • Indirection/dereferencing operator: * • * and & are inverses, They cancel each other out int y = 5; int *yPtr; yPtr = &y; /* yPtr gets address of y */ *yptr = 7; /* changes y to 7 */

4. Pass address of argument using & operator • Arrays are not passed with & • Used as alias/nickname for variable inside of function /*Function definition*/ void double( int *number ) { *number = 2 * ( *number ); } int main (void) { int a =5; /*Function call*/ double( &a ) printf(“%d /n”, a) } • Const qualifiers: variable can not be changed int *const myPtr = &x; /*Constant pointer*/ const int *myPtr = &x; /*Constant int*/ const int *const Ptr = &x; /*Cons. pointer point to Cons. int*/ Pass arguments to functions by reference by using pointer.

5. Sizeof: Returns size of operand in bytes • Can be used for program that depend on data type sizes and run on different system • Pointer Arithmetic: • ++, --, +,+=,-,-= • Operations meaningless unless performed on an array • Unit: base on array type and system int v[]; vPtr2 = v[ 2 ]; vPtr = v[ 0 ]; vPtr2 – vPtr = 2 vPtr = 3000; vPtr += 2; /*vPtr = vPtr2 = 3008; 1 unit = 4 bytes*/ sizeof Operator and Pointer Arithmetic.

6. Arrays and pointers closely related • Array name like a constant pointer • Pointers can do array subscripting operations • Equalities between pointer bPtr and array b[] • bPtr = b; • bPtr = &b[0]; • bPtr[3] = b[3]; • *( bPtr + 3 ) = b[3]; • Arrays of pointers • char *suit[ 4 ] = { "Hearts", "Diamonds", "Clubs", "Spades" }; The close relationships among pointers, arrays and strings.

7. Function pointers • Contains address of function • Function pointers can be • Passed to functions • Stored in arrays • Assigned to other function pointers • Two definition ways: • int *compare( int a, int b ) • Rerturn a pointer to int • int ( *compare )( int a, int b ) • Return an int Pointers to functions

8. 1. Relationship between pointers and arrays: • Fig. 7.24 in the lecture note • 2. Pointers to function: • Fig.7.26, 7.28in the lecture note Lab assignments • 3. Write a function largest that returns the largest value of an integer array and its position. For example, if an array contains { 13, 25, 80, 189, 30, 66, 4}, the function largest( ) should return the value 189 and its positions 3 (starting from 0). You are supposed to decide the arguments of the function. Suggestions (not mandatory) • Largest value can be returned by function • The positions of largest value can be returned by using pointers to pass arguments to function by reference