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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

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Overview of C

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  1. 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

  2. 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

  3. An Example of a C Program

  4. 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

  5. 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 #, /*, */, (, ), {, }, +, - *, /, %, ;, = [, ]

  6. Identifiers • 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

  7. 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

  8. 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 Examples kms = 1.609*miles;

  9. 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); fflush(stdin); getchar(); return (0); }

  10. 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;

  11. 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

  12. 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

  13. 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 ); getchar(); return 0; }

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