The C Programming

Lecture 24

Summary of Previous LectureProgramming in real life.

Introduction

What is Problem Solving? Problem Solving process.

Algorithm History Working Definition Examples

Algorithms to Programs

Summary of Previous LectureComponents of Algorithms

Variables and values Instructions Sequences Procedures Selections Repetitions Documentation

Software Development ProcessTop Down Algorithm Design

Today’s Lecture Algorithms and Programs

A C programming languageHistory of CC, A High level language

How to get started with C.Basic Structure of a C programData Storage and Data TypesVariables, Keywords, identifiers, Assignment

Today’s Lectureconstant variable

printf() and scanf() functions and usage Precedence

int and float Unary operations Increment and decrement operations

Today’s Lecture Comments Error and its Types Summary

From Algorithms to Programs

Both are sets of instructions on how to do a task Algorithm:

talking to humans, easy to understand in plain (English) language

Program: talking to computer (compiler) can be regarded as a “formal expression” of an

algorithm

A C Programming Language Flexible language:

Structured language Low level activities possible

It can produce lean and efficient code Wide availability on a variety of computers Widely used!

History of C CPL Combined Programming Language (Barron et al., 1963)

BCPL Basic CPL (Richards, 1969)

B (Thompson, 1970)

C K&R C (Ritchie, 1972)

ANSI C American National Standards Institute C (X3J11, 1989)

C99 (JTC1/SC22/WG14, ISO/IEC 9899, 1999)

A High-Level Language

Compilers and linkers translate a high level program into executable machine code.

#include <stdio.h>

int main(){ printf(“Hello World”);

return 0;}

Source code Executable code

10100110 0111011000100110 0000000011111010 1111101001001110 1010011011100110 1001011011001110 0010111010100110 0100111011111010 0110011001001110 10000110

etc...

How to get started? Download Turbo C++ Version 3.0 a free

software.http://turbo-c.soft32.com/ Install it!

Follow the step by step guide

for your first program!

Turbo C++ IDE Version 3

Click New to open a program window

Open a new window for writing a program

Output Message window

Set the Directories in Option Menu

Set the output directory path

Write your first program here

Write your program here!

Compile to find errors

Compile to check errors

No Errors Found

Execute the program by Run option

RUN to execute

See output by pressing Ctrl+F5

Output of your first program

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program: Pre Processor Directive include <stdio.h> file in this program! stdio.h

contains declaration of printf used in the

program

Example: Hello World

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program:

Program control is started from the main

function.

Example: Hello World

Main Function = Main Gate

You can enter the premises of the building through main gate! You can enter the premises of the building through main gate! Similarly program control is entered through main function..!Similarly program control is entered through main function..!

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program:

int indicates that only an integer value can come

out of this function

Example: Hello World

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program:

Curly braces mark the beginning and end of a

block of instructions.

Example: Hello World

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program:

Instruction (function call) to output “Hello World”.

This will print Hello World on the output screen

Example: Hello World

Basic Structure of a C Program

#include <stdio.h> int main(){

printf(“Hello World”);

return 0;}

C Program:

“Statements” (lines of instructions) always end with a semi-colon (;)

Example: Hello World

Where to store data? A data type is a representation of data that

defines a size and valid range for data. Built-in types: char, int, float Type modifiers: long, short, const User-defined types (arrays and records)

What about “strings”?Strings are arrays of char (discussed later)

Character Representation

Characters are stored as a small integer Each character has a unique integer

equivalent specified by its position in the ASCII table (pronounced “as-key”) American Standard Code for Information

Interchange

Character Representation

The ASCII values range from 0 to 127value 0: special character ’\0’

(a.k.a. NUL character)value 127: special character <DEL>other special characters:

’\n’ ’\t’ ’\’’ ’\\’ etc.various “extended” sets from 128 to 255

Remember: Variables

This jarcan contain

10 cookies

50 grams of sugar

3 slices of cake

etc.

ValuesVariable

• Are containers for values – places to store values

• Example:

Variable

Is a logical name for a container (an actual piece of computer memory for

values) Has a type associated with it

tells the computer how to interpret the bits Must be declared before use:

int i; float result;

int i=0; char initial=’K’;

Variable Declaration: Examples

int myID;

myID

Variable

Variable Declaration: Examples

int myID;

char myInitial = ’J’;

Single “forward quotes” or apostrophe (’) rather than

“back quotes” (‘)

Variable Declaration: Examples

int myID;

char myInitial = ’J’; 01001010myInitial

Variable Declaration: Examples

int myID;

char myInitial = ’J’;

char myInitial = 74 ;

01001010myInitial

Variable Declaration: Examples

float commission = 0.05;

short int myHeight = 183; /* cm */

long int mySalary = 100000000000000000000;

long float chanceOfADate = 3e-500;

double chanceOfA2ndDate = 1.5e-500;

float commission = 0.05;

short int myHeight = 183; /* cm */

long int mySalary = 100000000000000000000;

long float chanceOfADate = 3e-500;

double chance_of_a_2nd_date = 1.5e-500;

Variable Declaration: Examples

“Keywords”

Keyword

...has a special meaning in C ...is “case-sensitive” ...cannot be used as variable names Examples:

int, char, long, main, float, double, const, while, for, if, else, return, break, case, switch, default, typedef, struct, etc.

Variable Declaration: Examples

float commission = 0.05;

short int myHeight = 183; /* cm */

long int mySalary = 100000000000000000000;

long float chanceOfADate = 3e-500;

double chanceOfA2ndDate = 1.5e-500;

“Identifiers”

Identifier ...is a series of characters consisting of

letters, digits and underscores ( _) ...cannot begin with a digit ...must not be a keyword ...is “case-sensitive” Examples:

sUmoFA, x1, y2, _my_ID_, Main (careful!)

Assignment Puts a specified value into a specified

variable Assignment operator: =

<variable name> = <expression> ;

not to be confused with ==

Assignment: Examplesfloat x = 2.5 ;

char ch ;

int number ;

ch = ’\n’ ;

number = 4 + 5 ;

/* current value of number is 9. */

number = number * 2;

/* current value of number is now 18. */

Assignment Value must have a type assignable to the

variable Value may be automatically converted to

fit the new container Example:

various.c

#include <stdio.h>

/* Do various assignment statements */

int main(){ int integer;

char character;

float floatingPoint;

integer = 33;

character = 33;

floatingPoint = 33;

integer = 'A';

character = 'A';

floatingPoint = 'A';

integer = 33.33;

character = 33.33;

floatingPoint = 33.33;

integer = floatingPoint;

floatingPoint = integer;

return 0;

}

various.c

Constant Variables ...are variables that don’t vary ...may not be assigned to. ...must be initialized

const float Pi = 3.14159;

const int classSize = 100;

Constant Variables: Examplesconst int myID = 192;

myID = 666; /* Error! */

const int passMark = 80;

short char pAsSgRaDe = ’P’;

const float pi = 3.1415926; /* oops */

const double golden_ratio = 1.61803398874989;

Converts an angle from degrees to radians

output “Enter angle in degrees”

input angleInDegrees

angleInRadians = / 180 * angleInDegrees

output angleInRadians

#include <stdio.h>

/* Converts an angle in degrees to radians. */

const float PI = 3.1415926;

int main(){ float angleInDegs; float angleInRads;

printf("Enter angle in degrees:"); scanf("%f", &angleInDegs);

angleInRads = PI/180*angleInDegs;

printf("%f\n", angleInRads); return 0;}

Example: Constants

Example: Constants

“Global” constant variable

“Local” variables

more on this later...

#include <stdio.h>

/* Converts an angle in degrees to radians. */

const float PI = 3.1415926;

int main(){ float angleInDegs; float angleInRads;

printf("Enter angle in degrees: "); scanf("%f", &angleInDegs);

angleInRads = PI/180*angleInDegs;

printf("%f\n", angleInRads); return 0;}

Example: Constants

Print text on the screen

scanf function gets values from

user

#include <stdio.h>

/* Converts an angle in degrees to radians. */

const float PI = 3.1415926;

int main(){ float angleInDegs; float angleInRads;

printf("Enter angle in degrees: "); scanf("%f", &angleInDegs);

angleInRads = PI/180*angleInDegs;

printf("%f\n", angleInRads); return 0;}

Example: Constants

Result will be stored in

angleInRads

#include <stdio.h>

/* Converts an angle in degrees to radians. */

const float PI = 3.1415926;

int main(){ float angleInDegs; float angleInRads;

printf("Enter angle in degrees: "); scanf("%f", &angleInDegs);

angleInRads = PI/180*angleInDegs;

printf("%f\n", angleInRads); return 0;}

Example: Constants

Will be printed on the screen

#include <stdio.h>

/* Converts an angle in degrees to radians. */

const float PI = 3.1415926;

int main(){ float angleInDegs; float angleInRads;

printf("Enter angle in degrees: "); scanf("%f", &angleInDegs);

angleInRads = PI/180*angleInDegs;

printf("%f\n", angleInRads); return 0;}

printf() function In order to use printf(), function you need to include

<stdio.h> as #include<stdio.h>

To print an integer %d is used in printf

For example

This will print 9 on the output screen

printf() function To print a string on the screen %s is used in printf or

simply type words with printf.

For example This will print Hello world! This

is 9

printf() function To print a floating point number %f is used

For example

This will print 9.200000 on the

screen

printf() function Floating point with 2 digit precision, use %0.2f

For example

This will print 9.20 on the screen

scanf function Same include directive is used,

#include<stdio.h> Used to get a value from user at run time.

For example scanf(“%d”, &i);

Will get an integer value in the variable i. Can get character, floating or integer value

from the user.

scanf example Ask user to enter a value

scans the value

Prints the user input value on

the screen

Output of previous program

We have covered Type Variables Keyword and Identifiers Assignments Constant Variables

Precedence in Expressions

Defines the order in which an expression is evaluated

Precedence in Expressions -- Example

1 + 2 * 3 - 4 / 5 =

B stands for brackets, O for Order (exponents), D for division, M for multiplication, A for addition, and S for subtraction.

B.O.D.M.A.S.1 + (2 * 3) - (4 / 5)

More on precedence *, /, % are at the same level of precedence +, - are at the same level of precedence For operators at the same “level”, left-to-right

ordering is applied.2 + 3 – 1 = (2 + 3) – 1 = 42 – 3 + 1 = (2 – 3) + 1 = 0

2 * 3 / 4 = (2 * 3) / 4 = 6 / 42 / 3 * 4 = (2 / 3) * 4 = 0 * 4

Precedence in Expressions – Example

6.2

1 + 2 * 3 - 4 / 5 =

1 + (2 * 3) - (4 / 5)

Precedence in Expressions –Example..

6.2

1 + 2 * 3 - 4 / 5 =

1 + (2 * 3) - (4 / 5)

Precedence in Expressions – Example..

Integer division results in integer quotient

1 + 2 * 3 - 4 / 5 =

1 + (2 * 3) - (4 / 5)

Precedence in Expressions – Example

= 0

D’oh

1 + 2 * 3 - 4 / 5 =

1 + (2 * 3) - (4 / 5)

Precedence in Expressions ..

7

1 + 2 * 3 - 4 / 5 =

1 + (2 * 3) - (4 / 5)

int and float

float is a “communicable” type Example:

1 + 2 * 3 - 4.0 / 5

= 1 + (2 * 3) - (4.0 / 5)

= 1 + 6 - 0.8

= 6.2All integers are in Black

int and float – Example 2

(1 + 2) * (3 - 4) / 5

= ((1 + 2) * (3 - 4)) / 5

= (3 * -1) / 5

= -3 / 5

= 0

int and float – Example 2

(1 + 2.0) * (3 - 4) / 5

= ((1 + 2.0) * (3 - 4)) / 5

= (3.0 * -1) / 5

= -3.0 / 5

= -0.6

int and float – Example 3

(1 + 2.0) * ((3 - 4) / 5)

= (1 + 2.0) * (-1 / 5)

= 3.0 * 0

= 0.0

Unary operators Called unary because they require one operand. Example

i = +1; /* + used as a unary operator */

j = -i; /* - used as a unary operator */

The unary + operator does nothing, just emphasis that a numeric constant is positive.

The unary – operator produces the negative of its operand.

i=+1 is equal to i=i+1

Increment and decrement operators

++ is the increment operator i++;

is equivalent toi = i + 1;

-- is the decrement operatorj--;

is equivalent toj = j - 1;

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

/* Evaluate an expression */

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

/* Evaluate an expression */

int main(){

return 0;}

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

/* Evaluate an expression */

int main(){float result;

return 0;}

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

/* Evaluate an expression */

int main(){float result;

result = 1 + 2 * 3 - 4 / 5;

return 0;}

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

#include <stdio.h>

/* Evaluate an expression */

int main(){float result;

result = 1 + 2 * 3 - 4 / 5;printf(“%f\n”, result);

return 0;}

Example -- Simple Expressions

Evaluate an expression

set result to 1 + 2 * 3 - 4 / 5

output result

Output: 7.000000

#include <stdio.h>

/* Evaluate an expression */

int main(){float result;

result = 1 + 2 * 3 - 4 / 5;printf(“%f\n”, result);

return 0;}

Example -- Simple Expressions

Comments

Essential for documenting programs Run from a /* to the next */ Examples:

/* THIS IS A COMMENT */

/* So isthis */

/*** ...and this.***/

Comments ..

Comments do not “nest”

/* Comments start with a “/*”and end with a “*/”but they don’t nest! */

Errors in C Program Do not get Fear of an Error! All good programmers started with lot of

Errors Understand them and remove them!

Types of Errors In c program you may get

Syntax errorLogical errorRun time errors

Syntax Error These errors occur because of wrongly

typed statements, which are not according to the syntax or grammatical rules of the language. For example, in C, if you don’t place a semi-

colon after the statement (as shown below), it results in a syntax error.

printf(“Hello,world”)

Logical Error These errors occur because of logically

incorrect instructions in the program. Let us assume that in a 1000 line program, if

there should be an instruction, which multiplies two numbers and is wrongly written to perform addition.

This logically incorrect instruction may produce wrong results. Detecting such errors are difficult!

Run Time Errors These errors occur during the execution of the

programs though the program is free from syntax and logical errors.

Some of the most common reasons for these errors are When you instruct your computer to divide a number

by zero. When you instruct your computer to find logarithm

of a negative number. When you instruct your computer to find the square

root of a negative integer.

Summary High level language is converted into computer

understandable by a compiler. Compiler converts source code into computer

understandable code

C Programming is a way to program computers It has a syntax It has commands and structure

C can not be learnt! It can be understood by implementing it!