C Structures

1. C Structures

2. A first C Program • #include <stdio.h> • void main ( void ) • { float height, width, area, wood_length ; • scanf ( "%f", &height ) ; • scanf ( "%f", &width ) ; • area = 2 * height * width ; • wood_length = 2 * ( height + width ) * 3.25 ; • printf ( "The area of glass is : %f metres.\n", area ) ; • printf ( "The length of wood is : %f feet.\n", wood_length ) ; • }

3. Structures of program Explained • #include- Not a part of the program. Tells the compiler to get “something” – contents of a file needed for the program • stdio.h – standard input/output library • <>- tells the compiler to look in the system area as opposed to the “ “ –current directory • Void a keyword denoting nothing, tells the compiler that main returns nothing • Main- a special function. This function is ran at compilation time • (void)- tells the compiler that main works on nothing i.e. it has no parameters • { - brace divides the program into blocks.

4. Float- a variable type used to store values. Three types, floats, integers and characters. • ; - needed at end of all declarations in C, to keep compiler on track. Missing one causes tremendous errors. • Scanf- (scan formatted) function used for file input. • The parameters are placed in brackets. • “%f “- “” tells the compiler that everything inside is used to denote th string. % tells the compiler we are giving the format of a number and f tells the compiler it is of the float type. • &height – C does not allow the value of a parameter’s value to be changed. & tells the compiler to create a pointer to the given Variable, pass it to scanf

5. area=2 *height*width; - this is an assignment, the result of the expression is placed in area. • Printf –does the opposite if scanf (prints to console) • "The area of glass needed is : %f metres.\n", area)- The text is printed as is without dilimiters • %f tells the compiler a float will be printed, and the variable area tells the compiler what float to print • Other types • %d –signed decimal ineteger • %c – print a character • % 5d- decimal to five character positions • % %6.2 f floating point to 6 characters, right justified • \n- move to new line

6. Variables and data • Int variables- ranges from -32768 to +32767 with no fractional parts • Float varibles – real numbers of varying precision; -3.4E-38 to +32767 • Char variabes- can hold a single character • C does not provide Strings, Booleans

7. Declare A variable and assign values • int first; • float second; • char comma; • Type variablename ; • first = 100; • second=100.1; • char= l;

8. More Variables • typedef- Allows users to change the name of a standard data type. • enum- Enumerated data types enum color{red,blue,white} • struct- • Structures are heterogeneous user-defined datatypes • used to create nodes and lists ` e.g. Structbodyparts{ intfeet; double weight; char[5] eye_color; }

9. Magic Numbers • These are constants that can not be changed in a program e.g. array sizes, character positions, conversion factors, pi… • They should have their own names • We use the directive #define to manage magic numbers e.g. • #define pi 3.14159; • Now whenever the compiler sees pi it will send 3.14259

10. Expressions, Operands and Operators • Expressions are made from Opereands and operators • Operands things to work on i.e. variables • Operators the workers. • E.g. 2+ 4

11. Operators and Precedence • In Highest Priority order • - unary minus Makes number negative • * multiplication • / division • + addition • - subtraction • Use parenthesis to change precedence • A note ½ is not the same as ½.0 ..to overcome we use • int i = 3, j = 2 ; • float fraction ; • fraction = (float) i / (float) j ; • printf ( "fraction : %f\n", fraction ) ;

12. Conditional If • if (condition) • statement or block we do if the condition is true • else • statement or block we do if the condition is false

13. Relational Operators • == is equal • != not equal • < less than • > greater than • <= less than or equal to • >+ greater than or equal to • ! Not - used for inverting • && combine two statements that is both true • || or one of the statements is true

14. Loops • do …while - ran exactly one or more times • do • Statement or block • while (condition) • E.g • Do • printf ( "hello mum\n" ) ; • while (1) ;

15. While Loop (runs 0 or many times) • while (condition) • Statement or block e.g. while(1) printf (“hello mum”); For loop – repeats for a set number of times for ( i=0 ; i != 11 ; i = i+1 ) { printf ( "hello\n" ) ; }

16. Switch statement • Takes a value and decides which option to perform • Chooses the option that matches the case presented.

17. Switch statement(cont) • void main (void) • char selection ; • printf ("\nEnter the type of window : ") ; • scanf ("%c", &selection) ; • switch (selection){ case '1' : handle_casement (); • break ; • case '2' : handle_standard () ; • break ; • case '3' : handle_patio () ; • break ; • }

18. Functions • float get_ranged_value ( float min, float max ) // header • { • float temp ; • do { printf ( "Give the value : " ) ; • scanf ( "%f", &temp ) ; • } while ( (temp < min) || (temp > max) ) ; • return temp ; // return variable • } • Header – tells the compiler that we are creating a function called get_ranged_value, that returns a float, and accepts two float values • Return statement- tells the compiler what to send back to main

19. A note on arrays • Basically a box od data with subscripts to each element • Starts subscripts at 0 • Type arrayname[number of ellements] • e.gint x[10]; • creates and empty array that can hold 10 integers The number 10 is the subscript of the array. The elements of the array are X[0], x[1]…x[9]

20. Initializing an Array • int main() • { short age[4] = {23, 34, 65, 74}; • return 0; • } • Or • int main() • { short age[4]; • age[0]=23; • age[1]=34; • age[2]=65; • age[3]=74; • return 0; • }

21. Print an Array • for(j=0; j<4; j++) • printf("%d\n", same_age[j])