bil104e: introduction to scientific and engineering computing, spring 2005. lecture 2

Spring 2005, Gülcihan Özdemir Dağ Lecture 2: page 1

BIL104E: Introduction to Scientific and Engineering Computing, Spring 2005.

Lecture 2Outline2.1 Introduction2.2 Basics of C Programs

• Constants and Variables • Expressions • Statements and Statement blocks • C function types and names • Arguments to functions • The body of a function and Function calls

2.3 Another Simple C Program: Adding Two Integers2.4 Memory Concepts2.5 Data Types

• int• float• char

2.6 Arithmetic in C2.7 Keywords in C

Fall 2003, Gülcihan Özdemir Dağ Lecture 2: page 2

Before we go into detail of C programming Language Syntax let us look at the basic definitions:

• Constants and variables • Expressions • Statements • Statement blocks • C function types and names • Arguments to functions • The body of a function • Function calls

2.2 The Basics of the C Program


The Basics of the C Program

• As a building is made of bricks, a C program is made of basic elements, such as expressions, statements, statement blocks, and function blocks.

• But first, you need to learn two smaller but important elements, constant and variable, which make up expressions.

• Constants and Variables :– As its name implies, a constant is a value that never changes. A variable,

on the other hand, can be used to present different values.

• Expressions – An expression is a combination of constants, variables, and operators that

are used to denote computations. For instance, the following:

– (2 + 3) * 10 is an expression that adds 2 and 3 first, and then multiplies the result of the addition by 10. (The final result of the expression is 50.)

– Similarly, the expression 10 * (4 + 5) yields 90. The 80/4 expression results in 20.



• Expression Description – 6 An expression of a constant.

– i An expression of a variable.

– 6 + i An expression of a constant plus a variable.

– Exit(0) An expression of a function call.

• Arithmetic Operators As you've seen, an expression can contain symbols such as +, *, and /. In the C language, these symbols are called arithmetic operators.

Symbol Meaning

+ Addition

- Subtraction

* Multiplication

/ Division

% Remainder (or modulus)



• Among the arithmetic operators, the multiplication, division, and remainder operators have a higher precedence than the addition and subtraction operators. For example, the expression

2 + 3 * 10 yields 32, not 50.

Because of the higher precedence of the multiplication operator, 3 * 10 is calculated first, and then 2 is added into the result of the multiplication.

• As you might know, you can put parentheses around an addition (or subtraction) to force the addition (or subtraction) to be performed before a multiplication, division, or modulus computation. For instance, the expression

(2 + 3) * 10 performs the addition of 2 and 3 first before it does the

multiplication of 10.



• Statements – In the C language, a statement is a complete instruction, ending with a

semicolon. In many cases, you can turn an expression into a statement by simply adding a semicolon at the end of the expression.

– For instance, the following

i = 1; is a statement.

You may have already figured out that the statement consists of anexpression of i = 1 and a semicolon (;).

Here are some other examples of statements: i = (2 + 3) * 10; i = 2 + 3 * 10; j = 6 % 4; k = i + j;

Also, below are C statements. return 0; exit(0); printf ("Howdy, neighbor! This is my first C program.\n");



• Statement Blocks – A group of statements can form a statement block that starts with an opening

brace ({) and ends with a closing brace (}). A statement block is treated as a single statement by the C compiler.

– For instance, the following for(. . .) {

s3 = s1 + s2; mul = s3 * c;

remainder = sum % c; } is a statement block that starts with { and ends with }

• Anatomy of a C Function Functions are the building blocks of C programs. Besides the

standard C library functions, you can also use some other functions made by you or another programmer in your C program. In Hour 2 you saw the main() function, as well as two C library functions, printf() and exit(). Now, let's have a closer look at functions.


Function’s Anatomy



• Giving a Function a Valid Name – A function name is given in such a way that it reflects what the function

can do. For instance, the name of the printf() function means "print formatted data."

– There are certain rules you have to follow to make a valid function name. The following are examples of illegal function names in C:

– Illegal Name The Rule 2 (digit) A function name cannot start with a digit.

* (Asterisk) A function name cannot start with an asterisk.

+ (Addition) A function name cannot start with one of the

arithmetic signs that are reserved C keywords.

. (dot) A function name cannot start with ..

total-number A function name cannot contain a minus sign.

account'97 A function name cannot contain an apostrophe.


• Arguments to C Functions – You often need to pass a function some information before executing it. For example, in

first program, “Hello World.\n", is passed to the printf() function, and then printf() prints the string on the screen.

– Pieces of information passed to functions are known as arguments. The argument of a function is placed between the parentheses that immediately follow the function name.

– The number of arguments to a function is determined by the task of the function. If a function needs more than one argument, arguments passed to the function must be separated by commas; these arguments are considered an argument list.

– If no information needs to be passed to a function, you just leave the argument field between the parentheses blank.

• The Beginning and End of a Function – As you may have already figured out, braces are used to mark the beginning and end of a

function. The opening brace ({) signifies the start of a function body, while the closing brace (}) marks the end of the function body.

– As mentioned earlier, the braces are also used to mark the beginning and end of a statement block. You can think of it as a natural extension to use braces with functions because a function body can contain several statements.




• The Function Body – The function body in a function is the place that contains variable

declarations and C statements. The task of a function is accomplished by executing the statements inside the function body one at a time.

– Listing below demonstrates a function that adds two integers specified by its argument and returns the result of the addition.

• Listing: A function that adds two integers.

/* This function adds two integers and returns the result */

int integer_add( int x, int y ) {int result; result = x + y; return result;

}


The Basics of the C Program#include <stdio.h>

/* This function adds two integers and returns the result */int integer_add( int x, int y ){ int result; result = x + y; return result;}

int main(){ int sum; sum = integer_add( 5, 12); /* Function Call */

printf("The addition of 5 and 12 is %d\n", sum); return 0;}



• Summary – In this lesson you've learned the following: – A constant in C is a value that never changes. A variable, on the other hand, can

present different values. – A combination of constants, variables, and operators is called an expression in

the C language. An expression is used to denote different computations. – The arithmetic operators include +, -, *, /, and %. – A statement consists of a complete expression suffixed with a semicolon. – The C compiler treats a statement block as a single statement, although the

statement block may contain more than one statement. – The function type of a function determines the type of the return value made by

the function. – You have to follow certain rules to make a valid function name. – An argument contains information that you want to pass to a function. An

argument list contains two or more arguments that are separated by commas. – The opening brace ({) and closing brace (}) are used to mark the start and end

of a C function. – A function body contains variable declarations and statements. Usually, a

function should accomplish just one task.


2.3 Another Simple C Program:Adding Two Integers

1

2 /* Addition program */

3 #include <stdio.h>

4

5 int main()

6 {

7 int integer1, integer2, sum; /* declaration */

8

9 printf( "Enter first integer\n" ); /* prompt */

10 scanf( "%d", &integer1 ); /* read an integer */

11 printf( "Enter second integer\n" ); /* prompt */

12 scanf( "%d", &integer2 ); /* read an integer */

13 sum = integer1 + integer2; /* assignment of sum */

14 printf( "Sum is %d\n", sum ); /* print sum */

15

16 return 0; /* indicate that program ended successfully */

17 }

• 1. Initialize variables

• 2. Input

• 2.1 Sum

• 3. Print

• Program Output

Enter first integer45Enter second integer72Sum is 117



• As before– Comments, #include <stdio.h> and main

• int integer1, integer2, sum;– Declaration of variables

• Variables: locations in memory where a value can be stored

– int means the variables can hold integers (-1, 3, 0, 47)

– Variable names (identifiers)• integer1, integer2, sum

• Identifiers: consist of letters, digits (cannot begin with a digit) and underscores( _ )

– Case sensitive

– Declarations appear before executable statements• If an executable statement references and undeclared variable

it will produce a syntax (compiler) error



• scanf( "%d", &integer1 );– Obtains a value from the user

• scanf uses standard input (usually keyboard)

– This scanf statement has two arguments• %d - indicates data should be a decimal integer• &integer1 - location in memory to store variable• & is confusing in beginning – for now, just remember to include it

with the variable name in scanf statements

– When executing the program the user responds to the scanf statement by typing in a number, then pressing the enter (return) key



• = (assignment operator)– Assigns a value to a variable

– Is a binary operator (has two operands)sum = variable1 + variable2;

sum gets variable1 + variable2;

– Variable receiving value on left

• printf( "Sum is %d\n", sum );– Similar to scanf

• %d means decimal integer will be printed• sum specifies what integer will be printed

– Calculations can be performed inside printf statementsprintf( "Sum is %d\n", integer1 + integer2 );


2.4 Memory Concepts

• Variables – Variable names correspond to locations in the computer's

memory

– Every variable has a name, a type, a size and a value

– Whenever a new value is placed into a variable (through scanf, for example), it replaces (and destroys) the previous value

– Reading variables from memory does not change them

• A visual representation

integer1 45


2.5 Data Types : char• The char Data Type

– An object of the char data type represents a single character of the character set used by your computer. For example, A is a character, and so is a. But 7 is a number.

– But a computer can only store numeric code. Therefore, characters such as A, a, B, b, and so on all have a unique numeric code that is used by computers to represent the characters. Usually, a character takes 8 bits (that is, 1 byte) to store its numeric code.

– For many computers, the ASCII (American Standard Code for Information Interchange) codes are the de facto standard codes to represent a character set. The original ASCII character set has only 128 characters because it uses the lower 7 bits that can represent 27 (that is, 128) characters.

– On IBM-compatible PCs, however, the character set is extended to contain a total of 256 (that is, 28) characters. Appendix C, "ASCII Character Set," gives a list of the 256 characters.


2.5 Data Types : char• Character Constants

– A character enclosed in single quotes (`) is called a character constant. For instance, À', à', `B', and `b' are all character constants that have their unique numeric values in the ASCII character set. Given x as a character variable, for instance, the following two assignment statements are equivalent:

x = À'; x = 65; So are the following two statements:

x = à'; x = 97;

The Escape Character (\)In the C language, the backslash (\) is called the escape character; it tells

the computer that a special character follows. For instance, when the computer sees \ in the newline character \n, it knows that the next character, n, causes a sequence of a carriage return and a line feed. Besides the newline character, several other special characters exist in the C language, such as the following:

Character Description \b The backspace character; moves the cursor to the

left one character. \f The form-feed character; goes to the top of a new

page. \r The return character; returns to the beginning of

the current line. \t The tab character; advances to the next tab stop.


2.5 Data Types : int

• The int Data Type– You saw the integer data type in Hour 3. The int keyword is used to specify the

type of a variable as an integer. Integer numbers are also called whole numbers, which have no fractional part or decimal point. Therefore, the result of an integer division is truncated, simply because any fraction part is ignored.

– Depending on the operating system and the C compiler you're using, the length of an integer varies. On most UNIX workstations, for example, an integer is 32 bits long, which means that the range of an integer is from 2147483647 (that is, 231_1) to -2147483648. The range of a 16-bit integer is from 32767 (that is, 215_1) to -32768.

• Declaring Integer Variables– You also saw the declaration of an integer in Hour 3. The following shows the basic declaration

format:

– int variablename; Similar to the character declaration, if you have more than one variable to declare, you can use either the format like this

int variablename1; int variablename2; int variablename3; or like this:

int variablename1, variablename2, variablename3;


2.5 Data Types : float• The float Data Type

– The floating-point number is another data type in the C language. Unlike an integer number, a floating-point number contains a decimal point. For instance, 7.01 is a floating-point number; so are 5.71 and -3.14. A floating-point number is also called a real number.

– A floating-point number is specified by the float keyword in the C language. – Like an integer number, a floating-point number has a limited range. The ANSI standard

requires that the range be at least plus or minus 1.0*1037. Normally, a floating-point number is represented by taking 32 bits. Therefore, a floating-point number in C is of at least six digits of precision. That is, for a floating-point number, there are at least six digits (or decimal places) on the right side of the decimal point.

– Not like an integer division from which the result is truncated and the fraction part is discarded, a floating-point division produces another floating-point number. A floating-point division is carried out if both the divisor and the dividend, or one of them, are floating-point numbers.

• For instance, 571.2 / 10.0 produces another floating-point number, 57.12. So do 571.2 / 10 and 5712 / 10.0.

• Declaring Floating-Point Variables – The following shows the declaration format for a floating-point variable:

float variablename; float variablename1; float variablename2; float variablename3;

or like the following one:

float variablename1, variablename2, variablename3;


2.5 Data Types: Summary

Data Type C keyword Format specifier

İnteger int %d or %i

Charachter char %c

Floating (real) float %f

Double (long float) double %lf

For engineering notation use %e or %E

For hexadecimal representation use %x or %X

For octal representation use %o or %O


2.5 Data Types : Summary contiunes

• / (division operator) has special meaning in such:4/5 = 0 (int/int) pay attention to this

4/5.0 = 0.8 (int/float)

4.0/5 = 0.8 (float/int)

4.0/5.0 = 0.8 (float/float)

Type CASTING

(float) 4/5 0.8

(int) 3/6 0


2.5 Arithmetic

• Arithmetic calculations– Use * for multiplication and / for division

– Integer division truncates remainder• 7 / 5 evaluates to 1

– Modulus operator(%) returns the remainder • 7 % 5 evaluates to 2

• Operator precedence– Some arithmetic operators act before others (i.e., multiplication

before addition)• Use parenthesis when needed

– Example: Find the average of three variables a, b and c• Do not use: a + b + c / 3 • Use: (a + b + c ) / 3


2.5 Arithmetic

• Arithmetic operators:

• Rules of operator precedence:

C operation

Arithmetic operator

Algebraic expression

C expression

Addition + f + 7 f + 7

Subtraction - p – c p - c

Multiplication * bm b * m

Division / x / y x / y

Modulus % r mod s r % s

Operator(s) Operation(s) Order of evaluation (precedence)

() Parentheses Evaluated first. If the parentheses are nested, the expression in the innermost pair is evaluated first. If there are several pairs of parentheses “on the same level” (i.e., not nested), they are evaluated left to right.

*, /, or % Multiplication,Division, Modulus

Evaluated second. If there are several, they are evaluated left to right.

+ or - Addition Subtraction

Evaluated last. If there are several, they are evaluated left to right.


2.6 Keywords in C

• Keywords in C– Special words reserved for C

– Cannot be used as identifiers or variable names

Keywords

auto double int struct

break else long switch

case enum register typedef

char extern return union

const float short unsigned

continue for signed void

default goto sizeof volatile

do if static while

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