Agenda

1. Agenda • Computer Languages • Machine Language • High-Level Programming Language • Features of C Programming Language • How to Write a Simple C Program • How to Record a C Program (typescript)

2. Computer Programs • A program is a set of instructions to tell the computer what to do. • In order to better understand the programming process, we will first see how computer programs have developed over the past 50 years.

3. Computers • Computers are electronic devices that transfer and store data in wires (or gates). • Because the computer is an electronic device, the data within these wires or gates are either ON or OFF (like a light switch). • A collection of these ON and OFF combinations are used to represent data in the form of binary code(eg 010100001010111 )

4. Evolution of Programs • Early programmers needed to write programs using binary code or “machine language” to tell the computer to perform various tasks • Although the computer finds machine code efficient to perform tasks, early programmers found writing programs in machine code tedious and time-consuming.

5. Evolution of Programs • Grace Hopper, while working for the U.S. Navy in the 50’s developed a program to convert programs written in symbols to machine language - this was more convenient than writing a program using machine language. • This program used symbols to represent operations. Unfortunately, these programs didn’t work on all computers

6. Evolution of Programs • High-level languages were developed to allow the program to be run on many different computer systems. These “high-level” languages are considered “portable” programming languages since they can run on many different computers. • The programs are written in a form easily understood by the programmers (source code) and then a “compiler” program converts the source code into machine code to be run by the computer. • Examples of high-level languages: FORTRAN, COBOL & C

7. C Programming Language • The C programming language was developed by Dennis Ritchie at Bell AT&T labs in the early 1970s. • Dennis Ritchie and Ken Thompson used the C programming language to rewrite the UNIX operating system in 1973. • This contributed to the portability and popularity of C as UNIX operating system became widely accepted.

8. Features of C Programming Language • C is portable (can write and compile C programs on many different computer systems without major adjustments) • C is powerful, but also efficient. • C conforms to the ASNI standard for programming languages • C provides the basis for more complex programming languages such as C++

9. Steps to Create a Program • Step 1: Determine the requirements for the program (inputs, outputs, formulas) • Step 2: Plan out on paper the logic of the program (flowchart, pseudo code) • Step 3: Use Text editor to enter program (Source Code) • Step 4: Walk through program’s logic and syntax (look for errors) • Step 5: Compile the source code into an executable file • Step 6: Run the executable file & test the program’s logic as much as possible.

10. Debugging a Program • Debugging a program is the process of finding and removing errors from your program if it fails to compile or run properly • The compiler will NOT create an executable file if the source code contains syntax errors (but compiler will give error messages to help solve problem) • If you can compile your source code, errors can still occur due to improper logic, structure, or design approach.

11. Writing a Simple C Program Indicates to include a file that provides “standard input / output” functions (printf, scanf) which will be linked when source file is compiled • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • }

12. Writing a Simple C Program • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • } Indicates main function or “main part” of the program. All C programs have one main function. Note alllowercase. Syntax may also allow:main (void)int main (void)

13. Writing a Simple C Program • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • } Notice braces follow the main function. Other functions or commands are placed within these brackets to be executed when main function is run or “called” begin end

14. Writing a Simple C Program • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • } Notice how commands within braces are indented to “stand-out”. This allows programmers to be able to easily read code. Indenting is very important!

15. Writing a Simple C Program • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • } The printf command allows the display of output to be formatted: Some special codes include:\n - new line\t - tab (indent)\a - beep (alarm) Note: lowercase

16. Writing a Simple C Program • #include <stdio.h> • main () • { • printf (“Hello World!\n”); • } Most C commands end with a semi-colon.

17. Writing a Simple C Program • Task: • Write a C program to display the following information on a separate line: • Your name • Your student number • Your section • Tell us about yourself

18. Typescript • The script command in the Unix operating system is like a “tape recorder”: • Entering command script starts recording • all output on screen is saved to a file called typescript • Entering command exit stops recording • Refer to Assignment #0 for practice of printing out - Assignment is not for marks.