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Overview of C. A brief history of C programming language Preprocessor Keywords, special symbols, identifier Variable Names, data types, declarations, address, value Fundamental data types: integer, floating point, character Statements Assignment Arithmetic expression Functions and

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overview of c
Overview of C
  • A brief history of C programming language
  • Preprocessor
  • Keywords, special symbols, identifier
  • Variable
    • Names, data types, declarations, address, value
    • Fundamental data types: integer, floating point, character
  • Statements
    • Assignment
    • Arithmetic expression
  • Functions and
    • Main function
    • Function call
    • Input and output functions
  • Program style
  • Compilation and execution
  • Program errors
a brief history of c programming language
A Brief History of C Programming Language
  • Who, when and why?
    • C programming language was created by Dennis Ritchie at AT&T Bell Labs in 1972,
      • a successor of B which was created by Ken Thompson at Bell Labs
    • Purpose of C was to enable programmers to develop applications more efficiently
  • UNIX OS almost totally rewritten in C, 1973
  • ANSI made a standard for C in 1983
  • MSDOS was also written in C, 1984
preprocessor directives and comments
Preprocessor Directives and Comments
  • Preprocessor directives
    • A preprocessor is a program that modifies the program prior to its compilation
    • A line starts with #, provides an instruction to the preprocessor
    • Syntax:

# include <standard header file>

# define Name value

# include Name of another program file

    • Examples

#include <stdio.h>

#define KM_PER_MILE 1.609

#include ”file1.c”

  • Library
    • A collection of useful functions and symbols that may be accessed by a program.
      • scanf() and printf() are two functions in library stdio
  • Constant marco
    • A name that is replaced by a constant value in preprocessing
  • Comments
    • A comment is enclosed in /* and */, provides supplementary info, but is ignored by preprocessor and compiler
reserved words and special symbols
Reserved Words and Special Symbols
  • Reserved words (keywords) (See Appendix E)
    • A word that has special meaning in C. There are 40 reserved words in C
    • Data type

int, double, char, float, short, signed, unsigned, short, long, const, struct, union, typedef, static, extern

    • Flow control:

if, else, while, do, for, switch, case, default, break, continue, auto, return

  • Special symbols

#, /*, */, (, ), {, }, +, - *, /, %, ;, =

[, ]

  • Standard identifier
    • A word has a special meaning, but may be redefined.
    • Function names defined in ANSI C library: scanf, printf
  • User-defined identifiers
    • User defined names for constant, variable, function name
    • Rules in choosing an identifier
      • Must consists only of letters, digits, and underscores
      • Cannot begin with a digit
      • No reserved word
      • Not being used by standard library
      • Case sensitive
  • Examples:
    • Valid identifer: Letter1, LETTER1, letter_1, a2
    • Invalid identifer: letter-1, $money, 3mp, double
  • Convention: meaningful, simple, consistent.

miles, kms, area_of_circle, price_per_sq_in

variables data types and declarations
Variables, Data Types, and Declarations
  • What is a variable?
    • A variable represents a location in memory, whose value can be changed. A variable is used to hold data in a program
  • A variable has four parts: a name, a data type, address, and value. A variable must be declared before using
    • The name is expressed by user-defined identifier
    • Data type is a set of values and a set of operations on those values. The data type of a variable determines the number of memory cells required for the variable
      • Examples: int, double, char
variables data types and declarations con d
Variables, Data Types, and Declarations (con’d)
  • Declarations

A variable declaration tells the compiler the name and the kind of value stored in the variable. Must end with semicolon ; Examples

double kms;

double miles;  double kms, miles;

  • Address: after declaration, an address of the location in the memory is assigned, the first address of the memory cell in the location

For example the address of variable miles is &miles

  • The value of a variable is what stored in the variable. Much be assigned through assignment statement


kms = 1.609*miles;

test this example
Test this example

/* 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, kms;

/* Get and echo the distance in miles. */

printf("Enter a distance in miles>\n");

scanf("%lf", &miles);

printf("The distance in miles is %.2f.\n", miles);

/* Convert the distance to kilometers. */

kms = KMS_PER_MILE * miles;

/* Display the distance in kilometers. */

printf("That equals %.2f kilometers.\n", kms);

/* Display the address of miles and kms */

printf("The address of mile is %d\nThe address of kms is %d\n%", &miles, &kms);



return (0);


data types for integers
Data Types for Integers
  • How integers are represented in computers?
    • Only certain types of integers can be processed by C
    • Machine dependent
    • Example

int age;

data types for real numbers
Data Types for Real Numbers
  • Two data types for real numbers in C.
    • Single precision floating-point uses 32 bits represented in a fixed format (4 bytes)

e.g. 3.1415926 is represented in single precision as 1 10000000 10010010000111111011010

    • Double precision floating-point uses 64 bits

e.g. 3.1415926 is represented in double precision as

010000000000 100100100001111110110100110100010010110110000100

    • Delarations for single and double floating point variables

float miles;

double miles;

  • There are two ways to represent a real number in programs or display
    • Decimal format: 3.1415925
    • Exponential format

15.0e2  15.0 times 10 to the power 2 1500.0

15.0e-2  15.0 times 10 to the power -2 0.15

  • The differences in memory and what we write in program
data type for characters
Data Type for Characters
  • In computer a character is represented by 8 bits code such as ASCII using one memory cell
  • Each character corresponds to an integer in code(See Appendix A) http://www.lookuptables.com/

char c1, c2;

c1 = ’a’;

c2 = ’b’;

Note that the memory cell for c1 will store 97 in decimal, or in binary 01100001

example of data types
Example of Data Types

#include <stdio.h>

int main()


int apple;

double orange;

double pear;

char name;

apple = 5;

orange = 8.5;

pear = 94e-1;

name = 'a';

printf("I have %d kilo of apple %d\n\n", apple, &apple);

printf("I have %f kilo of orange %d\n\n", orange, &orange);

printf("I have %e kilo of orange\n\n", orange);

printf("I have %f kilo of pear %d\n\n", pear, &pear);

printf("I have %e kilo of pear\n\n", pear);

printf("I have %f kilo of pear\n\n", pear);

printf("My name is %c %d\n\n", name, &name);

printf("My name is %d \n\n", name);

printf( "\nPress Enter to continue..." );

fflush( stdin );


return 0;