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

2. 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

3. 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

4. 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
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ECE Application Programming: Lecture 16

5. 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 )
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ECE Application Programming: Lecture 16

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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
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ECE Application Programming: Lecture 16

14. ECE Application Programming: Lecture 16
Answer
Trgle w legs and has hyp of
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ECE Application Programming: Lecture 16

15. 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; }
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ECE Application Programming: Lecture 16

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

17. 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