EECE.2160 ECE Application Programming Instructor: Dr. Michael Geiger & Dr. Lin Li Spring 2019 Lecture 17: Functions

ECE Application Programming: Lecture 16 Lecture outline Announcements/reminders Program 4 due 3/21 Today’s lecture Functions 4/26/2019 ECE Application Programming: Lecture 16

ECE 160 - Introduction to Computer Engineering I 02/09/2005 Functions Functions used to break problem down into small, "bite-sized" pieces. Make code more manageable and readable Identify reusable pieces Functions have an optional type of return value, a name, and optional arguments Functions return at most, ONE value Functions must be either "prototyped" or declared prior to use. Good programming practices requires all functions to be prototyped. 4/26/2019 ECE Application Programming: Lecture 16 (c) 2005, P. H. Viall

ECE Application Programming: Lecture 16 Functions name of function type of value returned parameters of function (variables in) double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } Alternate way of writing above function double hyp(double a, double b) { return sqrt(a*a + b*b); } Single value returned by function 4/26/2019 ECE Application Programming: Lecture 16

Functions - complete program #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } prototype (note semi-colon ) actual function definition (NO semi-colon ) 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x ? y ? h ? a ? b ? sum ? result ? 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h ? a ? b ? sum ? result ? 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h ? a 3.0 b 4.0 sum ? result ? 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h ? a 3.0 b 4.0 sum 25.0 result ? 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h ? a 3.0 b 4.0 sum 25.0 result 5.0 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h ? a 3.0 b 4.0 sum 25.0 result 5.0 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Functions - scope #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; sum = a*a + b*b; result = sqrt(sum); return result; } x 3.0 y 4.0 h 5.0 4/26/2019 NOTE - a and b are NOT copied back to x and y ECE Application Programming: Lecture 16

Exercise - What prints (if 5, 12 entered) #include <stdio.h> #include <math.h> double hyp(double a, double b); void main() { double x,y,h; printf("Enter two legs of triangle: "); scanf("%lf %lf",&x,&y); h=hyp(x,y); printf("Trgle w legs %lf and %lf has hyp of %lf\n",x,y,h); } double hyp(double a, double b) { double sum, result; a = 3; b = 4; sum = a*a + b*b; result = sqrt(sum); return result; } x y h a b sum result 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Answer Trgle w legs 5.000000 and 12.000000 has hyp of 5.00000 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Example What does the following print? int f(int a, int b); int main() { int x = 1; int y = 2; int result1, result2, result3; result1 = f(x, y); result2 = f(y, result1); result3 = f(result1, result2); printf("x = %d, y = %d\n", x, y); printf("Result 1: %d\n", result1); printf("Result 2: %d\n", result2); printf("Result 3: %d\n", result3); return 0; } int f(int a, int b) { int i; // Loop index int r = 0; // Result for (i = 0; i < a; i++) r += b; return r; } 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Example solution x = 1, y = 2 Result 1: 2 Result 2: 4 Result 3: 8 4/26/2019 ECE Application Programming: Lecture 16

ECE Application Programming: Lecture 16 Final notes Next time More function examples (Monday, 3/18) Enjoy your Spring Break! Reminders: Program 4 due 3/21 4/26/2019 ECE Application Programming: Lecture 16