1. The C Programming
Lecture 24

2. Summary of Previous Lecture
Programming in real life.
Introduction
What is Problem Solving?
Problem Solving process.
Algorithm
History
Working Definition
Examples
Algorithms to Programs

3. Summary of Previous Lecture
Components of Algorithms
Variables and values
Instructions
Sequences
Procedures
Selections
Repetitions
Documentation
Software Development Process
Top Down Algorithm Design

4. Today’s Lecture Algorithms and Programs How to get started with C.
A C programming language
History of C
C, A High level language
How to get started with C.
Basic Structure of a C program
Data Storage and Data Types
Variables, Keywords, identifiers, Assignment

5. Today’s Lecture printf() and scanf() functions and usage Precedence
constant variable
printf() and scanf() functions and usage
Precedence
int and float
Unary operations
Increment and decrement operations

6. Today’s Lecture
Comments
Error and its Types
Summary

7. 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

8. 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!

9. 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)

10. A High-Level Language Source code Executable code
etc...
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }
Source code
Executable code
Compilers and linkers translate a high level program into executable machine code.

11. How to get started? Download Turbo C++ Version 3.0 a free software.
Install it!
Follow the step by step guide
for your first program!

12. Click New to open a program window
Turbo C++ IDE Version 3
Click New to open a program window

13. Open a new window for writing a program
Output Message window

14. Set the Directories in Option Menu

15. Set the output directory path

16. Write your first program here
Write your program here!

17. Compile to check errors
Compile to find errors
Compile to check errors

18. No Errors Found

19. Execute the program by Run option
RUN to execute

20. See output by pressing Ctrl+F5
Output of your first program

21. Basic Structure of a C Program
Example: Hello World
C Program:
Pre Processor Directive include <stdio.h> file in this program! stdio.h contains declaration of printf used in the program
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }

22. Basic Structure of a C Program
Example: Hello World
C Program:
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }
Program control is started from the main function.

23. Main Function = Main Gate
You can enter the premises of the building through main gate!
Similarly program control is entered through main function..!

24. Basic Structure of a C Program
Example: Hello World
C Program:
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }
int indicates that only an integer value can come out of this function

25. Basic Structure of a C Program
Example: Hello World
C Program:
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }
Curly braces mark the beginning and end of a block of instructions.

26. Basic Structure of a C Program
Example: Hello World
C Program:
Instruction (function call) to output “Hello World”. This will print Hello World on the output screen
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }

27. Basic Structure of a C Program
“Statements” (lines of instructions) always end with a semi-colon (;)
Example: Hello World
C Program:
#include <stdio.h>
int main() {
printf(“Hello World”);
return 0; }

28. 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)

29. 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

31. Character Representation
The ASCII values range from 0 to 127
value 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

32. Remember: Variables Are containers for values – places to store values
Example:
This jar
can contain
10 cookies
50 grams of sugar
3 slices of cake
etc.
Values
Variable
One form: strain the juices, put aside and let cool …(further instruction)… now add the reserved mix
In mathematics much more precisely: Call the sum of all items X. Call the number of items N… divide X by N 32

33. 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’;

34. Variable Declaration: Examples
int myID;
myID

35. Variable Declaration: Examples
int myID;
char myInitial = ’J’;
Single “forward quotes” or apostrophe (’) rather than “back quotes” (‘)

36. Variable Declaration: Examples
int myID;
char myInitial = ’J’;
myInitial

37. Variable Declaration: Examples
int myID;
char myInitial = ’J’;
char myInitial = 74 ;
myInitial

38. Variable Declaration: Examples
float commission = 0.05;
short int myHeight = 183; /* cm */
long int mySalary = ;
long float chanceOfADate = 3e-500;
double chanceOfA2ndDate = 1.5e-500;

39. Variable Declaration: Examples
float commission = 0.05;
short int myHeight = 183; /* cm */
long int mySalary = ;
long float chanceOfADate = 3e-500;
double chance_of_a_2nd_date = 1.5e-500;
“Keywords”

40. 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.

41. Variable Declaration: Examples
float commission = 0.05;
short int myHeight = 183; /* cm */
long int mySalary = ;
long float chanceOfADate = 3e-500;
double chanceOfA2ndDate = 1.5e-500;
“Identifiers”

42. 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!)

43. not to be confused with ==
Assignment
Puts a specified value into a specified variable
Assignment operator: =
<variable name> = <expression> ;
not to be confused with ==

44. Assignment: Examples float x = 2.5 ; char ch ; int number ;
ch = ’\n’ ;
number = ;
/* current value of number is 9. */
number = number * 2;
/* current value of number is now 18. */

45. Assignment Value must have a type assignable to the variable
Value may be automatically converted to fit the new container
Example:
various.c

46. 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

47. Constant Variables ...are variables that don’t vary
...may not be assigned to.
...must be initialized
const float Pi = ;
const int classSize = 100;

48. Constant Variables: Examples
const int myID = 192;
myID = 666; /* Error! */
const int passMark = 80;
short char pAsSgRaDe = ’P’;
const float pi = ; /* oops */
const double golden_ratio = ;

49. Example: Constants #include <stdio.h>
/* Converts an angle in degrees to radians. */
const float PI = ;
int main() {
float angleInDegs;
float angleInRads;
printf("Enter angle in degrees:");
scanf("%f", &angleInDegs);
angleInRads = PI/180*angleInDegs;
printf("%f\n", angleInRads);
return 0; }
Converts an angle from degrees to radians
output “Enter angle in degrees”
input angleInDegrees
angleInRadians =  / 180 * angleInDegrees
output angleInRadians

50. “Global” constant variable
#include <stdio.h>
/* Converts an angle in degrees to radians. */
const float PI = ;
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
“Global” constant variable
“Local” variables
more on this later...

51. Print text on the screen
#include <stdio.h>
/* Converts an angle in degrees to radians. */
const float PI = ;
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

52. Result will be stored in angleInRads
#include <stdio.h>
/* Converts an angle in degrees to radians. */
const float PI = ;
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

53. Will be printed on the screen
#include <stdio.h>
/* Converts an angle in degrees to radians. */
const float PI = ;
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

54. This will print 9 on the output screen
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

55. This will print Hello world! This is 9
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

56. This will print 9.200000 on the screen
printf() function
To print a floating point number %f is used
For example
This will print on the screen

57. This will print 9.20 on the screen
printf() function
Floating point with 2 digit precision, use %0.2f
For example
This will print 9.20 on the screen

58. 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.

59. scanf example Ask user to enter a value scans the value
Prints the user input value on the screen

60. Output of previous program

61. We have covered Type Variables Keyword and Identifiers Assignments
Constant Variables

62. Precedence in Expressions
Defines the order in which an expression is evaluated

63. Precedence in Expressions -- Example
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5)
B.O.D.M.A.S.
B stands for brackets,
O for Order (exponents),
D for division,
M for multiplication,
A for addition, and
S for subtraction.

64. More on 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 = 4
2 – = (2 – 3) + 1 = 0
2 * 3 / 4 = (2 * 3) / 4 = 6 / 4
2 / 3 * 4 = (2 / 3) * 4 = 0 * 4

65. Precedence in Expressions – Example
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5)
6.2

66. Precedence in Expressions –Example..
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5)
6.2

67. Precedence in Expressions – Example..
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5)
Integer division results in integer quotient

68. Precedence in Expressions – Example
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5)
D’oh
= 0

69. Precedence in Expressions ..
1 + 2 * / 5 =
1 + (2 * 3) - (4 / 5) 7

70. int and float float is a “communicable” type Example:
1 + 2 * / 5
= 1 + (2 * 3) - (4.0 / 5) =
= 6.2
All integers are in Black

71. int and float – Example 2 (1 + 2) * (3 - 4) / 5
= ((1 + 2) * (3 - 4)) / 5
= (3 * -1) / 5
= -3 / 5
= 0

72. int and float – Example 2 (1 + 2.0) * (3 - 4) / 5
= (( ) * (3 - 4)) / 5
= (3.0 * -1) / 5
= -3.0 / 5
= -0.6

73. int and float – Example 3 (1 + 2.0) * ((3 - 4) / 5)
= ( ) * (-1 / 5)
= 3.0 * 0
= 0.0

74. 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

75. Increment and decrement operators
++ is the increment operator
i++;
is equivalent to
i = i + 1;
-- is the decrement operator
j--;
j = j - 1;

76. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>

77. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>
/* Evaluate an expression */

78. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>
/* Evaluate an expression */
int main() {
return 0; }

79. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>
/* Evaluate an expression */
int main() {
float result;
return 0; }

80. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>
/* Evaluate an expression */
int main() {
float result;
result = * / 5;
return 0; }

81. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
#include <stdio.h>
/* Evaluate an expression */
int main() {
float result;
result = * / 5;
printf(“%f\n”, result);
return 0; }

82. Example -- Simple Expressions
Evaluate an expression
set result to
1 + 2 * / 5
output result
Output:
#include <stdio.h>
/* Evaluate an expression */
int main() {
float result;
result = * / 5;
printf(“%f\n”, result);
return 0; }

83. Comments Essential for documenting programs
Run from a /* to the next */
Examples:
/* THIS IS A COMMENT */
/* So is
this */ /*
** ...and this. ** */

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

85. Errors in C Program Do not get Fear of an Error!
All good programmers started with lot of Errors
Understand them and remove them!

86. Types of Errors In c program you may get Syntax error Logical error
Run time errors

87. 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”)

88. 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!

89. 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.

90. 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!