Week 2 Introduction to Computer and Algorithm (Part 2)

Transcription

1 Week 2 Introduction to Computer and Algorithm (Part 2) UniMAP Sem II-11/12 DKT121 1

2 Outline Pseudo code & flowchart Sample programming question Sample C program Identifiers and reserved words Program comments Pre-processor directives Data types and type declarations Operators Formatted input and output Program debugging 2

3 Sample Programming Question Write a program that calculates area of triangle. Your program should read the base length and the height length from user. Given the formula to calculate the area of triangle: 0.5 x (base) x (height). Steps: Analyze the problem Use algorithm Convert to actual codes 3

4 Recall..Pseudo code and Flowchart Try develop the pseudo code and flowchart for the problem given in the previous slide. 4

5 Sample C Program begin Variables declaration end /*Program name : program1.c Programmer : Yasmin This program calculates the area of triangle*/ #include <stdio.h> int main(void) { double dbase, dheight, darea; } printf( Enter base length : ); scanf( %f, &dbase); printf( Enter height length : ); scanf( %f, &dheight); darea=0.5 * dbase * dheight; printf( \narea of the triangle is : %5.2f\n, darea); return 0; return 0 (int) to OS Preprocessor directives Comments The term void indicates we receive nothing from OS and return an integer to OS body 5

6 Variables & Reserved Words Identifiers/Variables labels for program elements case sensitive can consist of capital letters[a..z], small letters[a..z], digit[0..9], and underscore character _ First character MUST be a letter or an underscore No blanks Reserved words cannot be variables/identifiers Reserved words already assigned to a pre-defined meaning e.g.: delete, int, main, include, double, for, if, etc. 6

7 Variables & Reserved Words An identifier for the data in the program Hold the data in your program Is a location (or set of locations) in memory where a value can be stored A quantity that can change during program execution 7

8 Constants A constant is a named or unnamed value, which does not change during the program execution. Example: const double dpi= Const int idegrees=360; Const char cquit= q ; Unnamed constant are often called literals Eg: and 360 8

9 Program Comments Starts with /* and terminates with */ OR Character // starts a line comment, if several lines, each line must begin with // Comments cannot be nested /* /* */*/ 9

10 Preprocessor Directives An instruction to pre-processor Standard library header: <stdio.h>,<math.h> E.g. #include <stdio.h> for std input/output #include <stdlib.h> Conversion number-text vise-versa, memory allocation, random numbers #include <string.h> string processing 10

11 Data Types Data types determine the following: Type of data stored Number of bytes it occupies in memory Range of data Operations that can be performed on the data Modifiers alter the meaning of the base type to more precisely fit a specific need C supports the following modifiers along with data types: short, long, signed, unsigned 11

12 Data Types & Memory Allocation Type Bits Bytes Range Char or Signed Char to +127 Unsigned Char to +255 Int or Signed int ,147,483,648 to +2,147,483,647 Unsigned int to +4,294,967,295 Short int or Signed short int ,768 to + +32,767 Unsigned short int to +65,535 Long int or signed long int ,147,483,648 to +2,147,483,647 Unsigned long int to +4,294,967,295 Float e-38 to 3.4 e+38 Double e-308 to 1.7e+308 Long Double e-308 to 1.7e

13 Variables Naming Conventions Variable names should use Hungarian notation Start with an appropriate prefix that indicates the data type After the prefix, the name of variable should have ore or more words The first letter of each word should be in upper case The rest of the letter should be in lower case. The name of variable should clearly convey the purpose of the variable 13

14 Naming Variables According to Standards Prefix Data Type Example i int and unsigned int itotalscore f float faveragescore d double dheight l long and unsigned long lfactorial c signed char and unsigned char cproductcode ai Array of integer aistudentid af Array of float afweight ad Array of double adamount al Array of long integer alsample ac Array of characters acmaterial 14

15 Data Types Declaration float fincome; float fnet_income; double dbase, dheight, darea; int iindex =0, icount =0; char cch= a, cch2; float income, net_income; Declare and initialize const float fepf = 0.1, ftax = 0.05; Named constant declared and initialized 15

16 Types of Operators Types of operators are: Arithmetic operators (+, -, *, /, %) Relational operators (>, <, ==, >=, <=,!=) Logical operators (&&, ) Compound assignment operators (+=, -=, *=, /=, %=) Binary operators: needs two operands Unary operators: single operand Bitwise operators: executes on bit level 16

17 Arithmetic Operators Used to execute mathematical equations The result is usually assigned to a data storage (instance/variable) using assignment operator ( = ) E.g. sum = marks1 + marks2; 17

18 Arithmetic Operators C Operation Arithmetic Operator Algebraic Expression C Expression Addition + f + 7 f + 7 Subtraction - p c p - c Multipication * bm b * m Division / x / y x / y Remainder (Modulus) % r mod s r % s 18

19 Exercise on Arithmetic Operators Given x = 20, y = 3 z = x % y = 20 % 3 = 2 (remainder) 19

20 Relational and Logical Operators Previously, relational operator: >, < >=, <=, ==,!= Previously, logical operator: &&, Used to control the flow of a program Usually used as conditions in loops and branches 20

21 More on relational operators Relational operators use mathematical comparison (operation) on two data, but give logical output e.g.1 let say b = 8, if (b > 10) e.g.2 while (b!= 10) e.g.3 if (mark == 60) print ( Pass ); Reminder: DO NOT confuse == (relational operator) with = (assignment operator) 21

22 More on logical operators Logical operators are manipulation of logic. For example: i. b=8, c=10, if ((b > 10) && (c<10)) ii. while ((b==8) (c > 10)) iii. if ((kod == 1) && (salary > 2213)) 22

23 Truth Table for && (logical AND) Operator exp1 false false true true exp2 false true false true exp1 && exp2 false false false true 23

24 Truth Table for (logical OR) Operator exp1 false false true true exp2 false true false true exp1 exp2 false true true true 24

25 Compound Assignment Operators To calculate value from expression and store it in variable, we use assignment operator (=) Compound assignment operator combines binary operator with assignment operator E.g. val +=one; is equivalent to val = val + one; E.g. count = count -1; is equivalent to count -=1; count--; --count; 25

26 Unary Operators Obviously operating on ONE operand Commonly used unary operators Increment/decrement { ++, -- } Arithmetic Negation { - } Logical Negation {! } Usually using prefix notation Increment/decrement can be both a prefix and postfix 26

27 Comparison of Prefix and Postfix Increments 27

28 Unary Operators (Example) Increment/decrement { ++, -- } prefix:value incr/decr before used in expression postfix:value incr/decr after used in expression val=5; Output: val=5; Output: printf ( %d, ++val); 6 printf ( %d, --val); 4 val=5; Output: val=5; Output: printf ( %d, val++); 5 printf ( %d, val--); 5 28

29 Operator Precedence Operators! + - (unary operators) * / % + - (binary operators) < <= >= > ==!= && = Precedence first second third fourth fifth sixth seventh last 29

30 Formatted Output with printf #include <stdio.h> void main (void) { } int imonth; float fexpense, fincome; imonth = 12; fexpense = 111.1; fincome = ; Declaring variable (imonth) to be integer Declaring variables (fexpense and fincome) to be real Assignment statements store numerical values in the memory cells for the declared variables, separates string literal from variable names printf ( Month=%2d, Expense=$%9.2f\n,iMonth,fExpense); Correspondence between variable names and %...in string literal 30

31 Formatted Output with printf 31

32 Formatted Input with scanf 32

33 Formatted Input with scanf 33

34 Program Debugging Syntax error Mistakes caused by violating grammar of C C compiler can easily diagnose during compilation Run-time error Called semantic error or smart error Violation of rules during program execution C compiler cannot recognize during compilation Logic error Most difficult error to recognize and correct Program compiled and executed successfully but answer wrong 34

35 Program Debugging-syntax error snapshot 35

36 Program Debugging-run time error snapshot 36

37 Program Debugging-logic error snapshot 37

38 End Week 2 Session 2 Q & A! 38