C Syntax and Semantics

Transcription

1 C Syntax and Semantics 1

2 C Program Structure C Language Elements Preprocessor directives Function Header, and Function body Executable statements Reserved word, Standard identifiers, user defined identifiers Data Types and Variable Declarations Expressions and Assignment in C 2

3 Input/Output operations Function Output function Input function Place holders Escape sequences Input/Output formatting Comments in C Example 3

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5 Function Header Function Body 5

6 C Program structure Example for Another C Program Write a program to Convert given distance in miles to kilometers. 6

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8 Are commands that give instructions to the C preprocessor Begins with a (#) as its nonblank character. C preprocessor is a system program that modifies a C program prior to its compilation Example #include <stdio.h> The C language cannot do I/O by itself, so we need help from the library stdio.h to use the screen/keyboard! We can use other libraries, too, as needed. Another popular library is math.h, for advanced math functions. 8

9 Examples #define KMS_PER_MILE # define # define VOTING_AGE 18 Define is a a preprocessor directives. Valid constant declarations A named constant is a location in memory that we can refer to by a name, and in which a data value that cannot be changed is stored. This directives instructs the processor to replace each occurrence of KMS_PER_MILE by

10 type of returned value name of function says no parameters int main ( ) 10

11 A C program is a collection of one or more functions (parts) There must be a function called main( ) A function body has two parts declaration and executable statements. Execution always begins with the first statement in function main( ) Any other functions in the program are subprograms and are not executed until they are called 11

12 printf( Hello, World ); This statement means: Display the words Hello, World on the screen return ( 0 ); This statement STOPs the program and returns Zero to the O.S. (more about this later) 12

13 Reserved Word A word that has special meaning in C Standard Identifiers A word having special meaning but one that a programmer may redefine (but redefinition is not recommended) User Defined Identifiers An identifier must consist only of letters, digits, and underscores. An identifier cannot begin with a digit A C reserved word cannot be used as an identifier. An identifier defined in a C standard library should not be redefined. C is a case-sensitive language. The names Pressure, pressure, and PRESSURE are not the same. 13

14 Invalid identifiers 1Letter double int TWO*FOUR joe s age# Age-of-cat Valid Identifiers Age_of_person taxratey2k PrintHeading begins with a number reserved word reserved word character * not allowed character not allowed character # not allowed character is not underscore character (_) 14

15 Reserved Word int void double return Standard Identifiers printf scanf User Defined Identifiers KMS_PER_MILE Miles 15

16 Integral Types Whole numbersdeclared as int, short, or long Int sample values 4578, -4578, 0 Floating Types Real numbers, declared as float, or double Float sample values Character Types Single characters, declared as char Char sample values B d 4? * 16

17 A string is a sequence of characters enclosed in double quotes Sample values Hello Year

18 Variable A name associated with a memory cell whose value can change. Variable Declaration Statements that communicate to the compiler the names of variables in the program and the type of information stored in each variable. 18

19 Giving a Value to a Variable You can assign (give) a value to a variable by using the assignment operator = VARIABLE DECLARATIONS char code ; int i; long national_debt; float payrate; double pi; VALID ASSIGNMENT STATEMENTS code = B ; i = 14; national_debt = ; pay_rate = 14.25; pi = ; 19

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21 An expression is a valid arrangement of variables, constants, and operators. In C each expression is evaluated to compute a value of a given type. The value of the expression is 14 21

22 Variable = Expression First, Expression on right is evaluated. Then the resulting value is stored in the memory location of Variable on left. Any information that was stored in the variable will be lost. NOTE: An automatic type conversion occurs after evaluation but before the value is stored if the types differ for Expression and Variable Example kms = KMS_PER_MILE * miles;

23 int a, b ; a = 5 ; b = 7 ; b = a + b ; a = b - 1 ; b = 3 ; 23

24 Printf (Output Function) The printf function displays the value of its format string after substituting in left-to-right order the values of the expressions in the print list for their list for their placeholders in the format string and after replacing escape sequences such as \n by their meanings. Scanf (Input Function) The scanf function copies into memory data entered during the program execution. The order of the placeholders must correspond to the order of the variables in the input list. The data must be entered in the same order in the input list. You should insert one or more blank characters or carriage returns between numeric items. 24

25 SYNTAX printf( format string, print list ) ; printf(format string); Examples : Place holder printf( That equals %f kilometers. \n, kms); printf( enter the distance in miles> ); printf( Hello, World?\n ); Escape sequence 25

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27 SYNTAX scanf( format string, input list ) ; Examples : Place holder scanf( %lf, &miles); Ampersand 27

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29 A placeholder is a symbol beginning with % in a format string that indicates where to display the output value Placeholder %c %d %f %lf Variable type char int double double Function use printf/scanf printf/scanf printf scanf 29

30 The backslash (\) is called an escape character Indicates that printf is supposed to do something unusual When encountering a backslash, printf looks to the next character and combines it with the backslash to form an escape sequence \n Start a new line of output \t tab printf( This is one line \n ); printf( and \n this \t is \t another \n ); This is one line and this is another 30

31 In C, you can control the APPEARANCE of number on the screen. Output formatting does not affect the VALUE of a variable, just how it appears to the user on the screen 31

32 Very simple: Add a number between the % and the d in the placeholder to specify the field length. Numbers will appear right-justified with preceding blanks if needed. 32

33 int len = 234 ; printf( Length is %5d, len); Output is: Length is 234 Note: The stands for a blank 33

34 Value Format Displayed Output Value Format Displayed Output 234 %4d %4d %5d %5d %6d %6d %1d %2d

35 We must indicate both the field width and the EXACT number of decimal places: %7.3 f minimum total field length Exact number of decimal digits Note: The decimal part will be rounded The whole part may be padded with blanks REMEMBER: The value of the number does not change, only its appearance 35

36 Double Formatting Displaying X using different %6.2f Value of x placeholder Displayed Output Value of x Displayed output

37 The simple placeholder %d will cause an integer value to be displayed with no leading blanks. A placeholder of the form %.mf has the same effect for values of type double. 37

38 Write a program to ask the user for the width and length of a piece of land and then tell him how many orange trees he can grow on it. Given that each orange tree requires 4 m 2. 38

39 #include <stdio.h> # define one_tree_space 4 void main() { int length,width, area, no_of_tree; printf( Enter length of the land> ); scanf( %d, &length); printf( Enter width of the land> ); scanf( %d, &width); area = length * width; no_of_tree = area / one_tree_space; printf( The available number of trees is %d trees\n, no_of_tree); } Programming Examples Example-1 39

40 Write a program to ask the user for the radius of a circle, and then display its area and circumference, displayed to 3 decimal digits. 40

41 #include <stdio.h> # define PI int main(void) { double radius, area, circumference; printf( Enterradius of the circle> ); scanf( %lf, &radius); area = PI * radius * radius; circumference = 2 * PI * radius; printf( The area of the circle = %.3f\n, area); printf( The circumference of the circle = %.3f\n, circumference); return(0); } 41

42 A comment is used to provide information, but it is ignored by the processor. Begin with /* and ends with */ /* Name : Foulan El Foulany */ /* This is a multi line comment */ 42

43 Write a program to create two integer variables, and store in them the values 3 and 5. Then calculate their sum and their product and display the result. 43

44 /* * Name: MMM * This program gets the sum and product of 2 integers */ #include <stdio.h> /* library containing printf */ int main ( ) { int first ; /* declaring first variable */ int second ; /* declaring second variable */ int sum ; /* variable to hold the sum */ int product ; /* variable to hold the product */ 44

45 first = 3 ; statement */ second = 5 ; /* assignment sum = first + second ; printf( The sum is %d \n, sum ); /* output */ product = first * second ; printf( The product is %d \n, product ); return (0); } 45

46 The sum is 8 The product is 15 46

47 /* * Name: NNN * This program gets the sum and product of 2 integers */ #include <stdio.h> /* library containing printf */ int main ( ) { int first = 3 ; /* declaring and assigning first variable */ int second = 5 ; /* declaring and assigning second variable */ int sum, product ; sum = fiirst + second ; product = first * second ; printf( The sum is %d \n The product is %d \n, sum, product ); } return ( 0 ) ; 47