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Lecture 04Chapter 2: Overview of C programming(cont..)

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Basic Data Types int used to declare numeric program variables of integer type

whole numbers, positive and negative

keyword: intint number;

 number = 12; Type of int format

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Basic Data Types cont… float

fractional parts, positive and negative

keyword: floatfloat height;

height = 1.72;

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Basic Data Types

sign exponent mantissa

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Basic Data Types cont…

Type Range in Typical Microprocessor

Implementation

 s ort − , .. ,

unsigned short 0 .. 65,535

int −2,147,483,648 .. 2,147,483,647

unsigned 0 .. 4,294,967,295

long −2,147,483,648 .. 2,147,483,647unsigned long 0 .. 4,294,967,295

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Basic Data Types cont… char equivalent to ‘letters’ in English language

Example of characters: Numeric digits: 0 - 9

Lowercase/uppercase letters: a - z and A - Z

S ace blank

Special characters: , . ; ? “ / ( ) [ ] { } * & % ^ < > etc single character keyword: char

char my_letter;

my_letter = 'U'; The declared character must beenclosed within a single quote!

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ASCII Code

American Standard Code for Information Interchange

particular code that specifies the integer representing each charvalue.

The digit characters '0' through '9' have code values of 48 through

57 (decimal). uppercase letters have the decimal code values 65 through 90

Lowercase letters have the decimal code values 97 through 122

the printable characters have codes from 32 (code for a blank orspace) to 126 (code for the symbol ~ ).

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ASCII Code Table

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Extended ASCII Code Table

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Constant example – volume of a cone#include

int main(void)

{double height, radius, base, volume;

double pi = 3.14;

printf(“Enter the height and radius of the cone:”);

 scanf(“%lf %lf”,&height, &radius);

base = pi * radius * radius;

volume = (1.0/3.0) * base * height;

printf(“\nThe volume of a cone is %lf ”, volume);

return 0;

}

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#define You may also associate constant using #define preprocessor directive

#include

#define PI 3.14int main(void){

double height, radius, base, volume;

printf(“Enter the height and radius of the cone:”);scanf(“%lf %lf ”,&height,&radius);

base = PI * radius * radius;volume = (1.0/3.0) * base * height;printf(“\nThe volume of a cone is %lf ”, volume);return 0;

}

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Input/Output Operations Input operation

an instruction that copies data from an input device intomemory

Output operation

 

the output devices (such as the monitor screen)

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Input/Output Functions A C function that performs an input or output operation

A few functions that are pre-defined in the header file stdio.hsuch as :

printf()

getchar() & putchar()

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The printf function Used to send data to the standard output (usually the

monitor) to be printed according to specific format. General format:

printf(“string literal”);

A sequence of any number of characters surrounded by double quotationmarks.

printf(“format string”, variables); Format string is a combination of text, conversion specifier and escape

sequence.

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The printf function cont… Example:

printf(“Thank you”);

printf (“Total sum is: %d\n”, sum); %d is a placeholder (conversion specifier)

marks the display position for a type integer variable

\n is an escape sequence moves the cursor to the new line

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Program Structure: Executablee.g. sum = sum + item;

Note: Left side of an assignmentstatement is called lvalue – it mustbe assignable

Examples of invalid assignment (result in compilation error “lvaluerequired as left operand of assignment”):

32 = a;

a + b = c;

Assignment can be cascaded, with associativity from right to left: a = b = c = 3 + 6; // 9 assigned to variables c, b and a

The above is equivalent to: a = (b = (c = 3 + 6));

which is also equivalent to:

c = 3 + 6;

b = c;

a = b;

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Program Structure: Executable Side Effect:

An assignment statement does not just assigns, it also has the

side effect of returning the value of its right-hand sideexpression

Hence a = 12; has the side effect of returning the value of

Usually we don’t make use of its side effect, but sometimes wedo, eg:

z = a = 12;  // or z = (a = 12);

The above makes use of the side effect of the assignment

statement a = 12; (which gives 12) and assigns it to z Side effects have their use, but avoid convoluted codes:

a = 5 + (b = 10);  // assign 10 to b, and 15 to a

Side effects also apply to expressions involving other operators

(eg: logical operators).

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Escape SequenceEscape Sequence Effect

\a Beep sound

\b Backspace

\f Formfeed (for printing)

\n New line

 \r Carriage return

\t Tab

\v Vertical tab

\\ Backslash

\” “ sign\o Octal decimal

\x Hexadecimal

\O NULL

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Placeholder / Conversion Specifier

No Conversion

Specifier

Output Type Output Example

1 %d Signed decimal integer 762 %i Signed decimal integer 76

3 %o Unsigned octal integer 134

4 %u Unsigned decimal integer 76

 

6 %X Unsigned hexadecimal (capital letter) 9C7 %f Integer including decimal point 76.0000

8 %e Signed floating point (using e

notation)

7.6000e+01

9 %E Signed floating point (using E

notation)

7.6000E+01

10 %g The shorter between %f and %e 76

11 %G The shorter between %f and %E 76

12 %c Character ‘7’

13 %s String ‘76'

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The scanf function Read data from the standard input device (usually keyboard)

and store it in a variable.

General format: scanf(“Format string”, &variable);

 

C address of operator it passes the address of the variable instead of the variable itself  tells the scanf() where to find the variable to store the new

value

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The scanf function cont… Example :

int age;

printf(“Enter your age: “);scanf(“%d”, &age);

 ommon onvers on en er use n pr n an scanfunctions.

printf scanf  

int %d %d

float %f %f  double %lf %lf  

char %c %c

string %s %s

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The scanf function cont… If you want the user to enter more than one value, you

serialise the inputs.

Example:

float height, weight;

printf(“Please enter your height and weight:”);scanf(“%f%f ”, &height, &weight);

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Few notes on C program cont… Reserved Words

Keywords that identify language entities such as statements,

data types, language attributes, etc.

Have special meaning to the compiler, cannot be used asidentifiers (variable, function name) in our pro ram. 

Should be typed in lowercase. Example: const, double, int, main, void,printf, while, for, else

(etc..)

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Few notes on C program cont… Punctuators (separators)

Symbols used to separate different parts of the C program. These punctuators include:

[ ] ( ) { } , ; “: * #

 

int main void()

{

int num = 10;

printf(“%d”, num);

return 0;

}

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Few notes on C program cont…Operators

Tokens that result in some kind of computation or action whenapplied to variables or other elements in an expression.

Example of operators:

  -

Usage example:

result = total1 + total2;

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Input/Output %d and %lf are examples of format specifiers; they are placeholders for values to be

displayed or read

Placeholder Variable Type Function Use%c char printf / scanf  

%d int printf / scanf  

 oa or ou e pr n

%f float scanf  

%lf double scanf  

%e float or double printf (for scientific notation)

Examples of format specifiers used in printf(): %5d: to display an integer in a width of 5, right justified

%8.3f : to display a real number (float or double) in a width of 8,

with 3 decimal places, right justified

Note: For scanf(), just use the format specifier without indicating width,

decimal places, etc.

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Input/Output \n is an example of escape sequence

Escape sequences are used in printf() function for certain special effects or to display

certain characters properly

These are the more commonly used escape sequences:

 

sequence\n New line Subsequent output will appear on the next line

\t Horizontal tab Move to the next tab position on the current line

\" Double quote Display a double quote "

%% Percent Display a percent character %

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Operators Arithmetic operations Binary Operators: +, – , *, /, % (modulo or remainder)

Left Associative (from left to right) 46 / 15 / 2 3 / 2 1

19 % 7 % 3 5 % 3 2

   – , Right Associative x = – 23 p = +4 * 10

Execution from left to right, respecting parentheses rule, and then precedencerule, and then associative rule (next page)

addition, subtraction are lower in precedence than multiplication, division, andremainder

Truncated result if result can’t be stored (the page after next)

int n; n = 9 * 0.5; results in 4 being stored in n.

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Operators Arithmetic operators: Associativity & Precedence

Operator Name Number of

operands

Position Associativity Precedence

( Parentheses Unary Prefix Left to right 1

) Parentheses Unary Postfix Left to right 1

+ Positive sign Unary Prefix Right to left 2

- Negative sign Unary Prefix Right to left 2++ Post-increment Unary Postfix Left to right 2

-- Post-decrement Unary Postfix Left to right 2

++ Pre-increment Unary Prefix Right to left 2

-- Pre-decrement Unary Prefix Right to left 2

*, /, % Multiplication,division,remainder

Binary Infix Left to right 3

+, - Addition, subtraction Binary Infix Left to right 4

=, +=, -=,*=, /=, %=

Assignment Binary Infix Right to left 5

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Operators Mixed-Type Arithmetic Operations

int m = 10/4; means

float p = 10/4; means

int n = 10/4.0; means

float q = 10/4.0; means

int r = -10/4.0; means Type Casting

Use a cast operator to change the type of an expression

syntax: (type) expression

int aa = 6; float ff = 15.8;

float pp = (float) aa / 4; means

int nn = (int) ff / aa; means

float qq = (float) (aa / 4);means

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Common Programming Errors Debugging Process removing errors from a

program

Three (3) kinds of errors :

 

Syntax Error a violation of the C grammar rules, detected during

program translation (compilation).

statement cannot be translated and program cannot beexecuted

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Common Programming Errors cont…Run-time errors

An attempt to perform an invalid operation, detectedduring program execution.

Occurs when the program directs the computer to,

by zero. The computer will stop executing the program, and

displays a diagnostic message indicates the line where the

error was detected

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Common Programming Errors cont… Logic Error/Design Error An error caused by following an incorrect algorithm

Very difficult to detect - it does not cause run-timeerror and does not display message errors.

The only sign of logic error – incorrect program

Can be detected by testing the program thoroughly,comparing its output to calculated results

To prevent – carefully desk checking the algorithmand written program before you actually type it

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Lecture 05:Chapter 3: Top-Down Design with Functions

CSE 115: Computing Concepts

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Top-Down Design and Structure Charts

Top down design

A problem solving method

break a problem up into its major subproblems

Solve the subproblems

  Derive the solution

Structure Charts

documentation tool shows the relationships among the subproblems of a

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Drawing Simple Diagrams PROBLEM: Draw some simple diagrams on your printer

or screen.

ANALYSIS: Both figures can be drawn with these fourbasic components:

■ a circle ■ parallel lines

■

a base line■

intersecting lines

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Draw a figure DESIGN : Divide the problem in three sub problems

INITIAL ALGORITHM

Draw a circle.

Draw a triangle.

  Draw intersecting.

ALGORITHM REFINEMENTS

Step 2 Refinement

2.1 Draw intersecting lines.

2.2 Draw a base.

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Structure Chart

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Top down design using function/* Draws a stick figure*/

#include /* printf definition */

/* function prototypes */

void draw_circle(void); /* Draws a circle */

void draw_intersect(void); /* Draws intersecting lines */

void draw_base(void); /* Draws a base line */

void draw_triangle(void); /* Draws a triangle */

int main(void)

{

/* Draw a circle. */draw_circle();

/* Draw a triangle. */

draw_triangle();

/* Draw intersecting lines. */

draw_intersect();return (0);

}

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A simple drawing program

Problem:- Write a program DrawFigures.c to draw a rocket ship (which is

a triangle over a rectangle, over an inverted V), a male stick

figure (a circle over a rectangle over an inverted V), and afemale stick figure (a circle over a triangle over an inverted V)

Analysis:

- No particular input needed, just draw the needed 3 figures- There are common shapes shared by the 3 figures

Design:

- Algorithm (view in words):1. Draw Rocket ship2. Draw Male stick figure (below Rocket ship)

3. Draw Female stick figure (below Male stick figure)

rocket male female

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A simple drawing program

Design (Structure Chart):

Draw 3Figures

Draw RocketShip

Draw TriangleDraw

Rectangle

Draw

Inverted V

Draw MaleStick Figure

Draw CircleDraw

Rectangle

Draw

Inverted V

Draw FemaleStick Figure

Draw Circle Draw TriangleDraw

Inverted V

rocket male female

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Modular Programming  Break a large problem into smaller pieces

Smaller pieces sometimes called ‘modules’ or ‘subroutines’ or‘procedures’ or functions

Why? Hel s mana e com lexit 

Smaller blocks of code Easier to read

Encourages re-use of code

Within a particular program or across different programs

Allows independent development of code Provides a layer of ‘abstraction’

a = sqrt(9.0);

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Functions The ‘building blocks’ of a C program

You’ve used predefined functions already:

main()

printf(), scanf(), pow()

User-defined functions

Your own code In combination with predefined functions

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Functions - Mathematical View

32)(

2++=

∆

 x x x f 

f(2)?isWhat

11is)2(

113443)2(2)2()2( 2

 f 

 f 

∴

⇒++⇒++⇒

)( x f 2 11

X Function

Returned

value

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Functions in CresultType functionName(type1 param1, type2 param2, …)

{

…

body 

…

} // functionName

If no result, resultType should be void 

Warning if not!

If no parameters, use void between ()

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Library Function Goal to write error-free code

Code reuse

C’s standard math library defines a function named sqrt -performs the square root computation

  e unct on ca n t e ass gnment statement

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C Library FunctionFunction Header Purpose: Example Argument(s) Result

abs(x) Returns the absolute value of its integer

argument: if x is −5 , abs(x) is 5

int int

ceil(x) Returns the smallest integral value that is notless than x : if x is 45.23 , ceil(x) is 46.0

double double

 .   . ,

cos(x) is 1.0 (radians)pow(x,y) double,

doubledouble

sqrt(x) Returns the nonnegative square root of x (1x)for x ≥ 0.0 : if x is 2.25 , sqrt(x) is 1.5

double double

log(x) Returns the natural logarithm of x for x > 0.0 :if x is 2.71828 , log(x) is 1.0

double double

log10(x) Returns the base-10 logarithm of x for x > 0.0: if x is 100.0 , log10(x) is 2.0

double double

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Using Functions Let int f(double x, int a) be (the beginning

of) a declaration of a function.

Then f(expr1, expr2) can be used in any expression

 –   . .,

 N = + d;

f(pi*pow(r,2), b+c)

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Using Functions Let int f(double x, int a) be (the beginning

of) a declaration of a function.

Then f(expr1, expr2) can be used in any expression

 –   . .,

 N = + d;

f(pi*pow(r,2), b+c)

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Using Functions (continued) Let int f(double x, int a) be (the beginning

of) a declaration of a function.

Then f(expr1, expr2) can be used in any

 expression where a value of type int can beused – e.g., N = f(pi*pow(r,2), b+c) + d;

Function f is executed and returns a

value of type intResult of f is added to d Sum is assigned to N

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Function definition Every function definition has the form

return-type function-name ( parameter declarations) {

definitions and statements

}

For practical purposes, code between {} (inclusive) is acompound statement

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Function Prototype There are many, many situations in which a

function must be used separate from where it is

defined – 

before its definition in the same C program

  In one or more completely separate C programs

This is actually the normal case!

Therefore, we need some way to declare a

function separate from defining its body. Called a Function Prototype

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Function Prototype (continued) Definition:– a Function Prototype in C is a language

construct of the form:– 

return-type function-name (parameter declarations) ;

I.e., exactly like a function definition, except with a

';' instead of a body in curly brackets

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Purposes of Function Prototype So compiler knows how to compile calls to that

function, i.e.,

number and types of arguments type of result

  “ ”

programmer who uses the function

As part of hiding details of how it works andexposing what it does.

A function serves as a “black box.”

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Header files In applications with multiple C programs, function

prototypes are typically provided in header files

I.e., the ‘.h’ files that programmers include in their code

Grouped by related functions and features

To make it easier for developers to understand

To make it easier for team development

To make a package that can be used by someone else

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Include #include

Search the system’s directories in order for a file of the

name foo.h

 " ".

Search the directory where the source program is foundfirst, before system directories

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Functions - Definition Structure Function 'header'

Return data type

(if any) Name Descriptive

Arguments (or parameter list) 

type function_name (type arg1, type arg2 )

{

statements;}

otice: ata type an name

Statements Variable declaration Operations Return value (if any)

double product(double x, double y)

{

double result;

result = x * y;return result;

}

A function that calculates the product of two numbers

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Functions - Example Function prototype

Like a variable declaration Tells compiler that the function will be defined

later

Helps detect program errors Note semicolon!!

Function definition See previous slide

Note NO semicolon

#include

/* function prototype */

double product(double x, double y);

int main()

{

double var1 = 3.0, var2 = 5.0; 

Function return

return statement terminates execution of thecurrent function

Control returns to the calling function

if return   expression; then value of expression is returned as the

value of the function call

Only one value can be returned this way

Function call   main() is the 'calling function'

 product() is the 'called function'

Control transferred to the function code

Code in function definition is executed

ans = product(var1, var2); printf("var1 = %.2f\n"

"var2 = %.2f\n",var1,var2);

 printf("var1*var2 = %g\n", ans);

}

/* function definition */

double product(double x, double y)

{

double result;

result = x * y;

return result;

}

Creating Function

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Creating Function

#include

#include

#define PI 3.14159

double circle_area(double diameter)

{

 

Functiondefinition

,

}

int main(void ) {

// identical portion omitted for brevity

// compute weight of a single washer

rim_area = circle_area(d2) - circle_area(d1);

unit_weight = rim_area * thickness * density;

// identical portion omitted for brevity

}

Calling circle_area()

twice.

Creating Function

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Creating Function

Components of a function definition

Header (or signature): consists of return type, function name, and a list of

parameters (with their types) separated by commas Function names follow identifier rules (just like variable names) May consist of letters, digit characters, or underscore, but cannot begin with a digit

Return type is void if function does not need to return any value Function body: code to perform the task; contains a return statement if return

type is not void

double circle_area(double diameter) {

return pow(diameter/2, 2) * PI;

}

Return type Function name Parameter

Function body

Programming style

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Programming style

Preferred practice: add function prototype Before main() function Parameter names may be omitted, but not their type

#include

#include

#define PI 3.14159

 Function prototype

double circle_area(double);

int main(void ) {

// identical portion omitted for brevity

// compute weight of a single washer

rim_area = circle_area(d2) - circle_area(d1);unit_weight = rim_area * thickness * density;

// identical portion omitted for brevity

}

double circle_area(double diameter)

{

return pow(diameter/2, 2) * PI;}

Functiondefinition