Tugas Alpro 3 cheapter 2

Overview of C

2.1 C Language Elements

Preprocessor Directives

preprocessor directive a C program line beginning with # that provides an instruction to the preprocessor. preprocessor a system program that modifies a C program prior to its compilation library a collection of useful functions and symbols that may be accessed by a program

/*

* Converts distances from miles to kilometers.

*/

#include <stdio.h>

 /* printf, scanf definitions */

#define KMS_PER_MILE 1.609

 /* conversion constant */

int

main(void)

{

double miles,

/* distance in miles kms;

 /* equivalent distance in kilometers */

/* Get the distance in miles. */

printf("Enter the distance in miles> ");

scanf("%lf", &miles);

/* Convert the distance to kilometers. */

kms = KMS_PER_MILE * miles;

/* Display the distance in kilometers. */

printf("That equals %f kilometers.\n", kms);

return (0);

constant macro a name that is replaced by a particular constant value before the program is sent to the compiler comment text beginning with /* and ending with */ that provides supplementary information but is ignored by the preprocessor and compiler.

Syntax Displays for Preprocessor Directives

#include Directive for Defining Identifiers from

Standard Libraries

SYNTAX: #include <standard header file>

EXAPLES: #include <stdio.h>

                 #include <math.h>

INTERPRETATION: #include directives tell the preprocessor where to find the meanings of standard identifiers used in the program. These meanings are collected in files called standard header files. ThMe header file stdio.h contains information about standard input and output functions such as scanf and printf. Descriptions of common mathematical functions are found in the header file math.h . We will investigate header files associated with other standard libraries in later chapters.

#define Directive for Creating Constant Macros

SYNTAX: #define NAME value

EXAMPLES: #define MILES_PER_KM 0.62137

                     #define PI 3.141593

                     #define MAX_LENGTH 100

INTERPRETATION: The C preprocessor is notified that it is to replace each use of the identifier

NAME by value . C program statements cannot change the value associated with NAME .

Function main

declarations the part of a program that tells the compiler the names of memory cells in a program executable statements program executable statements program lines that are converted to machine language instructions and executed by the computer

EXAMPLE: int

main(void)

{

printf("Hello world\n");

return (0);

}

Reserved Words

reserved word a word that has special meaning in C

Standard Identifiers

standard identifier a word having special meaning but one that a programmer may redefine (but redefinition is not recommended!)

2.2 Variable Declarations and Data Types

Variable Declarations

variable a name associated with a memory cell whose value can change variable declarations statements that communicate to the compiler the names of variables in the program and the kind of information stored in each variable.

Data Types

data type a set of values and operations that can be performed on those values.

Data Type double A real number has an integral part and a fractional part that

are separated by a decimal point. In C, the data type double is used to represent

real numbers (for example, 3.14159 , 0.0005 , 150.0 ). You can store a real number

in a type double variable, perform the common arithmetic operations (add,

subtract, multiply, and divide), and compare them.

The ASCII Code

ASCII code a particular code that specifies the integer representing each char value.

Assignment Statements

assignment statement an instruction that stores a value or a computational result in a variable

Input/Output Operations and Functions

input operation an instruction that copies data from an input device into memory output operation an instruction that displays information stored in memory input/output function a C function that performs an input or output operation. function call calling or activating a function. function argument enclosed in parentheses following the function name; provides information needed by the function format string in a call to printf, a string of characters enclosed in quotes ("), which specifies the form of the output line print list in a call to printf, the variables or expressions whose values are displayed placeholder a symbol beginning with % in a format string that indicates where to display the output value newline escape sequence the character sequence \n, which is used in a format string to terminate an output line.

Syntax Display for printf Function Call

SYNTAX: printf( format string, print list );

printf( format string );

EXAMPLES: printf("I am %d years old, and my gpa is %f\n",

age, gpa);

printf("Enter the object mass in grams> ");

1. Every C program has preprocessor directives and a main function. The main

function contains variable declarations and executable statements.

2. Variable names must begin with a letter or an underscore (the latter not recommended)

and consist of letters, digits, and underscore symbols. A reserved

word cannot be used as an identifier.

3. C’s data types enable the compiler to determine how to store a particular

value in memory and what operations can be performed on that value.

Three standard data types are int , d ouble , and char . The data type of each

variable must be declared.

4. The executable statements are derived from the algorithm and are translated

into machine language. Assignment statements are used to perform

computations and store results in memory. Function calls are used to get

data (function scanf ) and to display values stored in memory (function

printf ).