16.216 ECE Application Programming

1. 16.216ECE Application Programming Instructor: Dr. Michael Geiger Fall 2011 Lecture 4: Variables printf() introduction

2. Lecture outline • Announcements/reminders • Course home page: http://mgeiger.eng.uml.edu/16216/sp12/ • Discussion group on piazza.com • Search for “16.216”; remember, use Spring (not Winter) 2012 • Assignment 1 due 11:59 PM today • Source file name matters (prog1_simple.c)! • No .cpp files • No zipped archives of entire project • Submit only .c file • Assignment 2 posted, due 2/6 • Review: data representation • Number system basics • Constants • Types • Variables • Today • More on variables • Basic I/O ECE Application Programming: Lecture 4

3. Review: Number system basics • Base conversions • Use power rule to go from binary/hex to decimal • Use repeated division (or practice) to go from decimal to binary/hex • Representing data in C • Four basic data types • int, float, double, char • Constants • Discussed viable ranges for all types • #define to give symbolic name to constant ECE Application Programming: Lecture 4

4. Review: variables • Four basic data types • int, float, double, char • Variables • Have name, type, value, memory location • Variable declarations: examples • int x; • float a, b; • double m = 2.35; ECE Application Programming: Lecture 5

5. Variables - declaring main(){ float hours, payrate; float grosspay; int j; var name memory loc hours ? 4278 payrate ? 427C 4280 grosspay ? j ? 4284 ECE Application Programming: Lecture 4

6. Variables - assigning varname = expression; Declared variable single variable on left side of = expression any legal expression • Expression can be constant, variable, function call, arithmetic operation, etc. • Variable type (int, float, etc) and expression result type should match • If not, funny things can happen ... ECE Application Programming: Lecture 4

7. Variables (cont.) main(){ float hours, payrate; float grosspay; int j; hours = 40.0; var name memory loc hours 40.0 4278 payrate ? 427C 4280 grosspay ? j ? 4284 ECE Application Programming: Lecture 4

8. Variables (cont.) main(){ float hours, payrate; float grosspay; int j; hours = 40.0; payrate = 20.00; var name memory loc hours 40.0 4278 payrate 20.0 427C 4280 grosspay ? j ? 4284 ECE Application Programming: Lecture 4

9. Variables (cont.) main(){ float hours, payrate; float grosspay; int j; hours = 40.0; payrate = 20.00; grosspay = hours * payrate var name memory loc hours 40.0 4278 payrate 20.0 427C 4280 grosspay 800.00 j ? 4284 note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive). ECE Application Programming: Lecture 4

10. Variables (cont.) main(){ float hours, payrate; float grosspay; int j; hours = 40.0; payrate = 20.00; grosspay = hours * payrate j = 5; var name memory loc hours 40.0 4278 payrate 20.0 427C 4280 grosspay 800.00 j 5 4284 note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive). ECE Application Programming: Lecture 4

11. Variables (cont.) main(){ float hours, payrate; float grosspay; int j; hours = 40.0; payrate = 20.00; grosspay = hours * payrate j = 5; j = j + 1; var name memory loc hours 40.0 4278 payrate 20.0 427C 4280 grosspay 800.00 j 5 6 4284 note: referencing a variable only "reads" it (non-destructive). Assigning to a variable overwrites whatever was there (destructive). ECE Application Programming: Lecture 4

12. Example 1: Variables • What values do w, x, y, and z have at the end of this program? int main() { int w = 5; float x; double y; char z = ‘a’; x = 8.579; y = -0.2; w = x; y = y + 3; z = w – 5; return 0; } ECE Application Programming: Lecture 4

13. Example 1 solution int main() { int w = 5; float x; double y; char z = ‘a’; x = 8.579; y = -0.2; w = x; y = y + 3; z = w – 5; return 0; } w = 5 z = ‘a’ (ASCII value 97) x = 8.579 y = -0.2 w = 8 (value is truncated) y = (-0.2) + 3 = 2.8 z = 8 – 5 = 3 ECE Application Programming: Lecture 4

14. I/O basics • Need ability to • Print variables (or results calculated using them) • Read values from input • Output: printf() • Already seen basics • Input: scanf() ECE Application Programming: Lecture 4

15. printf() formatting • To print variables (or constants), insert %<type> in your format string • %c: single character • %d or %i: signed decimal integer • %u: unsigned decimal integer • %x or %X: unsigned hexadecimal integer • %f: float; %lf: double • Prints 6 digits after decimal point by default • %s: string ECE Application Programming: Lecture 2

16. examples - printf() float a=67.49,b=9.999925;printf("hello %f there %f\n",a,b);printf("%f%f%f%f\n",a,a,b,b);printf("a=%f, b=%f",a,b);printf("Cool huh?\n"); Printed: hello 67.490000 there 9.99992567.49900067.4990009.9999259.999925a=67.490000, b=9.999925Cool huh?

17. printf() example float a=67.49,b=9.999925;printf("hello %f there %f\n",a,b);printf("%f%f%f%f\n",a,a,b,b);printf("a=%f, b=%f",a,b);printf("Cool huh?\n"); Printed: hello 67.490000 there 9.99992567.49000067.4900009.9999259.999925a=67.490000, b=9.999925Cool huh? ECE Application Programming: Lecture 5

18. Next time • printf() and scanf()—more details ECE Application Programming: Lecture 4