16.216 ECE Application Programming

1. 16.216ECE Application Programming Instructor: Dr. Michael Geiger Fall 2012 Lecture 2: Basic C program structure Introducing data representations in C

2. Lecture outline • Announcements/reminders • Sign up for the course discussion group on Piazza • Program 1 due Monday, 9/10 • Basic C program structure • Preprocessor directives • Main program • Simple output • Readability: formatting, comments • Representing data in C • Number systems • Variables and constants ECE Application Programming: Lecture 2

3. Our first C program #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

4. Our first C program # indicates pre-processor directive include is the directive stdio.h is the name of the file to "insert" into our program. The <> means it is part of the C development system #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

5. Our first C program main is the name of the primary (or main) procedure. All ANSI C programs must have a main routine named main The () indicates that main is the name of a procedure. All procedure references must be followed with () #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

6. Our first C program { } enclose a "block". A block is zero or more C statements. Note that code inside a block is typically indented for readability—knowing what code is inside the current block is quite useful. #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

7. Our first C program printf() is a "built-in" function (which is actually defined in stdio.h). "Hello World!" is the string to print. More formally, this is called the control string or control specifier. #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} Every statement must end with a ";". Preprocessing directives do not end with a ";" (but must end with a return). ECE Application Programming: Lecture 2

8. Our first C program The \n is an escape character used by the printf function; inserting this character in the control string causes a “newline” to be printed—it’s as if you hit the “Enter” key #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

9. Our first C program The int tells the compiler our main() program will return an integer to the operating system; the return tells what integer value to return. This keyword could be void, indicating that the program returns nothing to the OS. #include <stdio.h>int main(){ printf("Hello World!\n"); return 0;} ECE Application Programming: Lecture 2

10. Variations #1 of first program #include <stdio.h>int main(){ printf("Hello"); printf("there"); printf("World!"); return 0;} ECE Application Programming: Lecture 2

11. Variations #2 of first program #include <stdio.h>int main(){ printf("Hello\n"); printf("there\n"); printf("World!\n"); return 0;} ECE Application Programming: Lecture 2

12. Variations #3 of first program #include <stdio.h>int main(){ printf("Hello\nthere\nWorld!\n"); return 0;} ECE Application Programming: Lecture 2

13. Variations #4 of first program #include <stdio.h>int main(){printf ("Hello\nthere\nWorld!\n");return 0;} Note while this is syntactically correct, it leaves much to be desired in terms of readability. ECE Application Programming: Lecture 2

14. Code readability • Readability wouldn’t matter if: • Entire code project written by one person • All code was in same file • Same person is the only one to use the code • Code was used only for a short period of time • More typically: • Projects are split—multiple programmers and files • Code usually reused • Multiple users • Used/adapted (hopefully) over long period of time • You may reuse code ... but forget what you originally wrote! • Bottom line: code needs to be readable ECE Application Programming: Lecture 2

15. Comments • C allows you to add comments to your code • Single line comments: start with // • Multi-line comments: start with /* end with */ • Typical uses • Multi-line comment at start of program with • Author’s name (& other info if appropriate) • Date started/modified • File name • Description of overall file functionality • For individual code sections • Single/multi-line comment for major section of code performing single function • Single line comment for single line of code if that line alone is important ECE Application Programming: Lecture 2

16. Comment example /* 16.216 ECE Application Programming Instructor: M. Geiger 11/8/2014 hello.c: Intro program to demonstrate basic C program structure and output */ #include <stdio.h> // Standard I/O library /* Main program: prints basic string and exits */ int main() {printf("Hello World!\n"); return 0; } ECE Application Programming: Lecture 2

17. Representing data in C • Two major questions (for now) • What kind of data are we trying to represent? • Data types • Can the program change the data? • Constants vs. variables ECE Application Programming: Lecture 2

18. Four Types of Basic Data • Integer int • Floating point (single precision) float • Double Precision double • Character char ECE Application Programming: Lecture 2

19. Integer Constants • Any positive or negative number without a decimal point (or other illegal symbol). • Legal values: 5 -10 +251000 253 -26351 +98 • Illegal values:2,523 (comma) 6.5 (decimal point)$59 (dollar sign) 5. (decimal point) ECE Application Programming: Lecture 2

20. Range of Integers (Machine Dependent) unsigned signed • char 0  255 -128  +127 (8 bits) • short int 0  65535 -32768  + 32767short (16 bits) • int 0 to 4294967295 -2147483648  2147483647 longlong int (32 bits) ECE Application Programming: Lecture 2

21. float/double Constants • Any signed or unsigned number with a decimal point • Legal values: 5. .6 +2.70.0 -6.5 +8. 43.4 • Legal (exponential notation):1.624e3 7.32e-2 6.02e23 1.0e2-4.23e2 +4.0e2 1.23e-4 +11.2e+7 • Illegal: $54.23 6,349.70 1.0E5 ECE Application Programming: Lecture 2

22. float/double Constants • Range of float (32 bits) ± 1.175494351 E – 38 ± 3.402823466 E + 38 • Range of double (64 bits)± 2.2250738585072014 E – 308± 1.7976931348623158 E + 308 ECE Application Programming: Lecture 2

23. Character Constants • Stored in ASCII or UNICODE • Signified by single quotes (’ ’) • Valid character constants ’A’ ’B’ ’d’ ’z’ ’1’ ’2’’!’ ’+’ ’>’ ’?’ ’ ’ ’#’ • Invalid character constants’GEIGER’ ’\’ ’CR’ ’LF’ ’’’ ’’’’ ’”’ ”Q” ECE Application Programming: Lecture 2

24. Character Escape Sequences ECE Application Programming: Lecture 2

25. Using #define with constants • Often makes sense to give constant value a symbolic name for readability • Don’t want constant wasting memory space • Use #define to define a macro • Macro: named code fragment; when name is used, the preprocessor replaces name with code • Syntax: #define <name> <code> • Common use: defining constants • By convention, start constant values with capital letters • e.g. #define NumberOne 1 • At compile time, all uses of “NumberOne” in your program are replaced with “1” and then compiled ECE Application Programming: Lecture 2

26. Next time • Continue discussing data in C • Remember: Program 1 due next Monday, 9/10 ECE Application Programming: Lecture 2