Lecture Slides on Passing Variables | CSE A205, Study notes of Engineering

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CSE294A

Introduction to C Programming for Engineers

Lecture

Jeffrey Miller, Ph.D.

Passing Variables

Pass by Value

When a variable is passed by value into a function, the value of thevariable passed in is copied into the value of the variable in theparameter list

Any change that occurs to the function’s parameter in the functiondoes not affect the value of the variable in the calling function

void

func(int

num)

num

} void

main()

int

num

func(num); printf

(“%d”,

num);

Pointers

Pointers enable programs to simulate call-by-reference and to create and manipulate dynamicdata structures (which are data structures that cangrow and shrink at run time)

Pointers are variables whose values are memoryaddresses

All of the scalar variables we have discussedcontain specific values, not memory addresses

Pointer Declarations

To create a pointer, use the *

int *count_ptr;

count_ptr is then a pointer to an object of type int

To create an int variable, we use

int count;

Then, to say that count_ptr contains the address of the count variable,we use

count_ptr = &count;

The & is the way we get the memory address of a variable

When the * is used in any line

after

the declaration, it is called

dereferencing

Dereferencing will get the value at the address contained within thevariable

Pass by Reference

Using pointers, we can now get the same effect of passing variables byreference

void change_value (int *my_ptr)

*my_ptr

} void change_value (int val)

val

} void main()

int value

int *value_ptr; value_ptr

&value; printf (“%d”, value);

what is printed? change_value(value); printf (“%d”, value);

what is printed? change_value(value_ptr); printf (“%d”, value);

what is printed? change_value(&value); printf (“%d”, value);

what is printed? }

Program

Write a program to display the values of the address, value,and dereferenced values of pointers and scalar variables tobetter understand the * and & characters, as well aspointers.