16.216 ECE Application Programming

16.216ECE Application Programming Instructor: Dr. Michael Geiger Fall 2013 Lecture 14 Functions

Lecture outline • Announcements/reminders • Program 4 due today • Program 5 to be posted; due 10/16 • Exam regrades due 10/11 • Today’s lecture • Functions • Early feedback forms ECE Application Programming: Lecture 14

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. ECE Application Programming: Lecture 14

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 ECE Application Programming: Lecture 14

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 ) ECE Application Programming: Lecture 14

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 ? ECE Application Programming: Lecture 14

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 ? ECE Application Programming: Lecture 14

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 ? ECE Application Programming: Lecture 14

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 ? ECE Application Programming: Lecture 14

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 ECE Application Programming: Lecture 14

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 NOTE - a and b are NOT copied back to x and y ECE Application Programming: Lecture 14

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 ECE Application Programming: Lecture 14

Answer Trgle w legs 5.000000 and 12.000000 has hyp of 5.00000 ECE Application Programming: Lecture 14

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; } ECE Application Programming: Lecture 14

Example solution x = 1, y = 2 Result 1: 2 Result 2: 4 Result 3: 8 ECE Application Programming: Lecture 14

Final notes • Next time • Continue discussion of functions • Pointers • Reminders: • Program 4 due today • Program 5 to be posted; due 10/16 • Exam regrades due 10/11 ECE Application Programming: Lecture 14

16.216 ECE Application Programming