Lecture4.pdf

Getting Started with C By Sashika Kumarasinghe  Lesson Objectives You will learn, The importance of learning C language. Variables, Constants and Keywords. Different Parts of C program. IN 1101 Programming Fundamentals 2 Why bother to...

Getting Started with C By Sashika Kumarasinghe  Lesson Objectives You will learn, The importance of learning C language. Variables, Constants and Keywords. Different Parts of C program. IN 1101 Programming Fundamentals 2 Why bother to learn C? Foundation for Modern Languages: Many modern programming languages, such as C++, Java, and C#, have their syntax and features rooted in C, making it the foundation for understanding these languages. System Programming: C is extensively used for developing operating systems, compilers, and other system-level software. The major parts of Windows, Unix, Linux, and Android operating systems are written in C. Embedded Systems: C is the language of choice for programming microcontrollers and embedded systems due to its efficiency and low-level access capabilities. Education and Research: C remains a core part of computer science education, providing students with a deep understanding of fundamental programming concepts and hardware interaction. Open-Source Projects: Numerous open source projects, including the Linux kernel and many core libraries, are written in C, contributing to its continued relevance and popularity. Variables, Constants and Keywords Variable – A data storage location that has a value that can change during program execution. Constant – Fixed value that can’t change. Keyword – A word that carries special meaning. IN 1101 Programming Fundamentals Understanding Computer Memory Computer uses random-access memory (RAM) to store information while it is operating. RAM is volatile. Each byte of memory in RAM has a unique address. Unique address can be used to distinguish the bytes of memory from other bytes. IN 1101 Programming Fundamentals IN 1101 Programming Fundamentals 6 IN 1101 Programming Fundamentals 7 Variables A variable is a named data storage location in your computer’s memory. Rules for constructing variables names: The name can contain letters (a to z and A to Z), digits (0 to 9), and the underscore character (_). No commas or blanks are allowed within a variable name. The first character in the variable name must be an alphabet or underscore ( _ ). Case matters. General styles to create long variables- Using an underscore to separate words or using camel notation. e.g. Variable name Legality Sum ✓ 4sale × savings#account × SavingsAccount ✓ Savings_Account ✓ IN 1101 Programming Fundamentals Variable Declarations & Initializing Before you use a variable in a C program, it must be declared. A variable declaration has the following form : typename varname; e.g. int count; float percent, total; H/W Location of variable declarations in the source code is important. WHY ? Initialization: Before using a variable, you should always initialize it to a known value. Can do this independently of the variable declaration by using an assignment statement. int count; count = 0; You can also initialize a variable when it’s declared int count = 0; IN 1101 Programming Fundamentals Constants Constant - value stored in a constant can’t be changed during program execution. IN 1101 Programming Fundamentals Symbolic Constants Symbolic constants are constants which are represented by name or symbol in a C program. Defining symbolic constants : Using #define directive #define CONSTANTNAME literal E.g. #define PI 3.14159 Using const keyword E.g. const int count = 100 IN 1101 Programming Fundamentals Literal Constants Literal Constant – A value that is types directly into the source code whenever it is needed. e.g. const int = 50 ; is a constant integer expression where 50 is an integer literal Four types of literals: Integer literals Float literals Character literals String literals IN 1101 Programming Fundamentals C Keywords break double return case else long Keywords are the words whose meaning has already been explained to the C compiler. char for register Keywords cannot be used as variable names. const float static default if switch IN 1101 Programming Fundamentals  # include The first C int main( ) Program{ int p, n ; float r, si ; p = 1000 ; n=3; r = 8.5 ; si = p * n * r / 100 ; printf ( "%f\n" , si ) ; return 0 ; } IN 1101 Programming Fundamentals Comments in C Program Comments are used in a C program to clarify either the purpose of the program or the purpose of some statement in the program. e.g // Calculation of simple interest (ANSI C permits this comment) IN 1101 Programming Fundamentals What is main()? main() is a function. main() function is an entry point of the programming code to start its execution. main() is a universally accepted keyword, therefore cannot change its meaning and name. Return type is defined before main(). If main() function returns an integre value -→ int main() The integer value returning is 0 and it indicates success. If main() function returns nothing → void main() IN 1101 Programming Fundamentals Variables and their Usage Any variable used in the program must be declared before using it.For example, int p, n ; float r, si ; IN 1101 Programming Fundamentals printf() Output to screen is achieved using readymade library functions like printf(). For us to be able to use the printf( ) function, it is necessary to use #include at the beginning of the program. #include is a preprocessor directive. The general form of printf( ) function is, printf ( "", ) ; can contain, %f for printing real values %d for printing integer values %c for printing character values E.g. printf ( "%f", si ) ; printf ( "%d %d %f %f", p, n, r, si ) ; IN 1101 Programming Fundamentals scanf() scanf() can be used to get user inputs through the keyboard during program execution. scanf ( "%d %d %f", &p, &n, &r ) ; ampersand (&) before the variables in the scanf() function is a must and gives the location number (address) used by the variable in memory IN 1101 Programming Fundamentals Summary You learned, The importance of learning C language. Variables, Constants and Keywords. Different Parts of C program. IN 1101 Programming Fundamentals 20 Questions? 21 IN 1101 PROGRAMMING FUNDAMENTALS