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Today’s Material

Today’s Material. Why C? History of C Generic C Program Structure Variables Type and Name Assignment Operator Simple I/O scanf/printf. Why C?. Simple and Structural Minimal syntax Availability and Portability C compilers are available for a wide range of platforms

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Today’s Material

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  1. Today’s Material • Why C? • History of C • Generic C Program Structure • Variables • Type and Name • Assignment Operator • Simple I/O • scanf/printf

  2. Why C? Simple and Structural Minimal syntax Availability and Portability C compilers are available for a wide range of platforms Windows, UNIX, embedded systems Language of choice for system programming Most OS code are written in C Widely known Almost every programmer knows C There are lots of public code written in C

  3. History of C C evolvedas follows: CPL Combined Programming Language (Barron, 1963) BCPL Basic CPL (Richards, 1969) B (Thompson, 1970) C (Kernighan & Ritchie, 1972) ANSI C American National Standards Institute C (X3J11, 1989)

  4. Generic C Program Structure #include <stdio.h> /* main designates the starting place of our program */ main() { /* Variables hold Data Items Needed in the Program */ Variable Declarations; /* Steps of our program: I/O, computation (expressions) */ Statement1; Statement2; … StatementN; } /* end-of-the program */

  5. Start Prompt the user for a temperature Get the fahrenheit temperature celsius = (fahrenheit-32)/1.8 Print the fahrenheit and celsius degrees End First C Program PROBLEM Convert a fahrenheit temperature to celsius #include <stdio.h> /* Convert fahrenheit to celsius */ main() { float fahrenheit; float celsius; printf(“Enter a temp in fahrenheit: “); scanf(“%f”, &fahrenheit); celsius = (fahrenheit-32)/1.8; printf(“%f degrees fahrenheit equals %f degrees celsius\n”, fahrenheit, celsius); }

  6. First C Program Dissected #include <stdio.h> /* Convert fahrenheit to celsius */ main() { float fahrenheit; float celsius; printf(“Enter a temp in fahrenheit: “); scanf(“%f”, &fahrenheit); celsius = (fahrenheit-32)/1.8; printf(“%f degrees fahrenheit equals %f degrees celsius\n”, fahrenheit, celsius); } Load the standard library to handle I/O Comments: In between /* …. */ main(): Designates where the execution will start Curly braces Determines the beginning and the end of a code block

  7. First C Program Dissected (cont) #include <stdio.h> /* Convert fahrenheit to celsius */ main() { float fahrenheit; float celsius; printf(“Enter a temp in fahrenheit: “); scanf(“%f”, &fahrenheit); celsius = (fahrenheit-32)/1.8; printf(“%f degrees fahrenheit equals %f degrees celsius\n”, fahrenheit, celsius); } • Variables • A variable is a memory location whose contents can be filled and changed during program execution • float is the variable type • fahrenheit & celsius are variable names • Statements • Steps of your program. • Statements end with a semicolon (;)

  8. First C Program Dissected (cont) #include <stdio.h> /* Convert fahrenheit to celsius */ main() { float fahrenheit; float celsius; printf(“Enter a temp in fahrenheit: “); scanf(“%f”, &fahrenheit); celsius = (fahrenheit-32)/1.8; printf(“%f degrees fahrenheit equals %f degrees celsius\n”, fahrenheit, celsius); } Output Use printf function to print something on the screen Input Use scanf function to read something from the keyboard Computation Use mathematical operators to perform computation

  9. prog.c COMPILER prog.s ASSEMBLER printf.o prog.o scanf.o LINKER prog.exe LOADER + OS program running From C Code-2-Machine Code • Now that we have our C program, how does it get translated to machine code, i.e., to 0s and 1s • Remember a computer understands just 0s and 1s • We use several system software components to translate out C program to machine code • Compiler, assembler, linker, loader+OS

  10. First C Program Executed PROGRAM #include <stdio.h> /* Convert fahrenheit to celsius */ main() { float fahrenheit, celsius; printf(“Enter a temp in fahrenheit: “); scanf(“%f”, &fahrenheit); celsius = (fahrenheit-32)/1.8; printf(“%f degrees fahrenheit equals %f degrees celsius\n”, fahrenheit, celsius); } /* end-main */ DATA fahrenheit 75.4 ? ? celsius 24.11 ? Enter a temp in fahrenheit: 75.4 degrees fahrenheit equals 24.11 degrees celsius 75.4

  11. number1 number2 What’s a Variable? • A memory location whose contents can be filled and changed during program execution • Each variable has a type and name • Type defines the type of information that can be stored in that memory location • Nameis a label that allows us to refer to that memory location Memory name • intnumber1; /* stores a natural number (152) */ • floatnumber2; /* stores a real number (65.324) */

  12. Variable Declaration • The basic format for declaring variables is datatype varName, varName, ... ; where datatype may be int/* Stores a natural number, e.g., 34532 */ float/* Stores a real number, e.g., 15.342 */ double/* Also stores a real number, but more precision */ /* e.g., 345.22359573943 */ char/* Stores an ASCII char, e.g., ‘A’ */

  13. Variable (Identifier) Names • C identifiers consist of letters and digits in any order, except that: • The first character must be a letter • fahrenheit, celsius, sum, a123, i1, i2, i3 • The identifier can be in lowercase or uppercase • The upper and lower cases may be mixed • sum, Sum, SUM • The underscore (_) can be included and it can also be the first char of the identifier • total_sum, num_students, _localVar

  14. Variable (Identifier) Names (cont) • C identifiers consist of letters and digits in any order, except that: • The identifiers should not contain a blank space, hyphen or quotes • “sum” : quotes(“) is illegal • total-sum : illegal character ( - ) • total sum : blank space should not be there • Identifier names are case-sensitive • sum, Sum and sUm are all different identifiers

  15. Variable Examples & Assignment int x; /* Define 1 int */ float fahrenheit, celsius; /* Define 2 floats */ double d; /* Define 1 double */ x = -85; /* Assign -85 to x */ d = 3.4545673; /* Assign 3.4545673 to d */ fahrenheit = 75.0; /* Assign 75.0 to fahrenheit */ celsius = 23.4; /* Assign 23.4 to celsius */ • = is the assignment operator • Syntax: identifier = value; • Changes the contents of the memory location that the variable refers to 75.0 3.4545673 -85 23.4 x fahrenheit d celsius

  16. Variable Declaration & Initialization • Variables can be initialized during declaration int sum = 32000; /* can be positive */ int x = -23, y = 458; /* and negative */ float f1 = 34.5; float fahrenheit = 75.3, celsius = 0; double d1, d2 = -4.567; /* Can be negative */ double d3 = 5e+3; /* Scientific notation: 5x10^3 */ d1 = 675e-4; /* 675x10^-4 = 0.0675 */ 32000 -23 458 34.5 75.3 0.0 0.0675 -4.567 5000 sum x y f1 celsius fahrenheit d1 d2 d3

  17. Character Variables • Represents a single character • Characters are letters of the alphabet (both upper and lower case) • Ten digits 0 through 9 • Special symbols such as + $ . , - ! • Characters need to be enclosed in single quotes • e.g. 'A' char letter; letter = 'A'; /* Letter A */ letter = ‘9’; /* Digit 9 */ char letter = ‘c’; /* initialization */

  18. Character Variables (more) • In fact, char corresponds to 1 byte natural number • char type variables occupy 1 byte in memory • What’s really stored in a char variable is the ASCII value of the character • ASCII value of ‘A’ is 65 • ASCII value of ‘B’ is 66 • ASCII value of ‘0’ is 48 • ASCII value of ‘1’ is 49 • http://www.asciitable.com/

  19. ASCII Table

  20. Special Characters • Characters are enclosed in single quotes • How do I denote a single quote?  char letter; letter = ''';  char letter; letter = '\''; • When a backslash (\) is used in front of a character, the combination is called an Escape Sequence

  21. Escape Sequences • Combinations of a backslash (\) and a character that tells the compiler to escape from the ways these character would normally be interpreted • Commonly used escape sequences • \n move to next line • \t move to next tab setting • \\ backslash character • \' single quote • \" double quote

  22. sizeof Operator • You can learn the number of bytes that a certain type occupies in memory using the sizeof operator int a = sizeof(char); /* Returns 1 */ int b = sizeof(short); /* Returns 2 */ int c = sizeof(int); /* Returns 4 */ int d = sizeof(long); /* Returns 4 or 8 */ int e = sizeof(float); /* Returns 4 */ int f = sizeof(double); /* Returns 8 */ 1 2 4 8 4 4/8 a b e f c d

  23. Keyboard Input/ Display Output • Achieved using scanf/printf functions • Definitions of these functions are in <stdio.h> • So we must include these definitions at the start #include <stdio.h> int main() { scanf(); printf(); } /* end-main */

  24. printf/scanf Functions • Formatted input/output functions in C • Definitions in standard I/O library <stdio.h> • If we are using these functions in our programs, we must include these definitions by #include <stdio.h> at the beginning of our programs printf(FormatString, expression1, expression2, …); scanf(FormatString, &variable1, &variable2, …); • FormatString is enclosed in double quotes • “abcdxyz” • “number is %d\n” • Format specification %d is used to print an int

  25. printf Examples int x = 45; float y = 56.7; printf(“What’s up?\n”); /* Print a msg only */ printf(“Number x: %d, 2 times y: %f\n”, x, y); printf(“Sum of x and y is %f\n”, x+y); Expression section Format section What’s up? Number x: 45, 2 times y: 56.70000 Sum of x and y is 101.7000

  26. printf Format Specifiers

  27. printf Examples printf(“First line.\nSecond line. Percent char %% XYZ\n”); printf(“3rd line. Slash \\, single quote \`\n”); printf(“4th line. Double quote \”. End\n”); printf(“Line 5. char A: %c, ASCII value: %d\n”, ‘A’, ‘A’); printf(“Line 6. Tab\tTab.\n”); printf(“Line 7. Carriage return:\rOK\n”); printf(“Line 8.\n”); First line. Second line. Percent char % XYZ 3rd line. Slash \\, single quote ` 4th line. Double quote “. End Line 5. char A: A, ASCII value: 65 Line 6. Tab Tab. OKne 7. Carriage return: Line 8.

  28. printf Examples char c1 = ‘A’, c2 = ‘c’, c3 = ‘9’, c4 = ‘\\’; int x = 11, y = 16; float f = 56.7; double d = 456.789345; printf(“c1 is <%c>, c2 is <%c>, c3: <%c>, c4: <%c>\n”, c1, c2, c3, c4); printf(“x is <%d>, y is <%d>, avg is <%d>\n”, x, y, (x+y)/2); printf(“Sum of <%f> and <%lf> is <%lf>\n”, f, d, f+d); c1 is <A>, c2 is <c>, c3: <9>, c4: <\> x is <11>, y is <16>, avg is <13> Sum of <56.70000> and <456.7893450000000> is <513.4893450000000>

  29. printf: Specifying Field Length & Justification char c1 = ‘A’, c2 = ‘c’; int x = 11, y = 16; float f = 56.7; double d = 456.789345; printf(“+-------+-------+\n”); printf(“|%7c|%-7c|\n”, c1, c2); printf(“|%-7d|%7d|\n”, x, y); printf(“|%7.2f|%-7.1lf|\n”, f, d); Printf(“+-------+-------+\n”); +-------+-------+ | A|c | |11 | 16| | 56.70| 456.7| +-------+-------+

  30. More printf Examples printf("%.9f\n", 300.00145678901f); printf("%.19lf\n", 300.0014567890123456789); 300.001464844 300.0014567890123700000 float has 7 digit precision here (3000014) double has 16 digits (3000014567890123)

  31. scanf Examples • “%c” char • “%d” int • “%f” float • “%lf” double char c; int x; float y; double d; scanf(“%d”, &x); /* Read 1 int */ scanf(“%c”, &c); /* Read 1 char */ scanf(“%f”, &y); /* Read 1 float */ scanf(“%lf”, &d); /* Read 1 double */ /* Read 1 int, 1 float, 1 double */ scanf(“%d%f%lf”, &x, &y, &d); Variable Address Format section

  32. getchar and putchar Functions • getchar reads a single character from the keyboard • putchar writes a single character on the screen • Example: char c; printf(“What-to-do Menu \n”); printf(“ (a) To write a C program \n”); printf(“ (b) To go swimming \n”); printf(“ (c) To watch TV \n”); printf(“Select one option: ”); c = getchar(); /* Read the user choice */ getchar(); /* Skip newline ‘\n’ char */ putchar(‘B’); /* Prints B on the screen */ c = ‘Z’; putchar(c); /* prints Z on the screen */

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