C/C++ Functions Mark Redekopp 2 A QUICK LOOK 3 Function - PowerPoint PPT Presentation

1 C/C++ Functions Mark Redekopp

2 A QUICK LOOK

3 Function Signatures/Prototypes • Also called procedures or methods • We think of a function as a blackbox (don't know or care how it does the task a b internally) where we can provide inputs and get back a value max • A function has: – A name int max(int a, int b); – Zero or more input parameters Function Signature/Prototype – 0 or 1 return (output) values • We only specify the type • The signature (or prototype ) of a function specifies these aspects so others know how to "call" the function

4 User Defined Functions #include <iostream> • using namespace std; We can define our own functions // prototype / declaratoin • Good practice is to "declare" your int max(int a, int b); function by placing the prototype int main() (signature) at the top of your code { int x, y, mx; • "Define" the function (actual code cin >> x >> y; implementation) anywhere by /* Code for main */ placing the code in { } • As shown it is defined but never used (no one actually "calls" the } max function) // Definition int max (int a, int b) { • At most 1 return value if(a > b) – void = 0 return values return a; // immediately stops max else • Return value is substituted at the return b; // immediately stops max site of the function call and used in } the larger expression

5 Execution of a Function #include <iostream> • using namespace std; Statements in a function are executed // prototype / declaratoin sequentially by default int max(int a, int b); • Defined once, called over and over int main() • Functions can call other functions { int x, y, mx; – Goes and executes that collection of code cin >> x >> y; // say "6 103" then returns to continue the current function /* Code for main */ • Compute max of two integers 6 z = max(x,4); Each call causes the program to pause the cout << z << endl; current function, go to the called function 103 cout << max(x, y) << endl; and execute its code with the given return 0; arguments then return to where the calling } function left off, • Return value is substituted in place of the // Definition int max (int a, int b) function call { if(a > b) return a; else return b; }

6 Anatomy of a function void printMenu() • Return type (any valid C type) { cout << “Welcome to ABC 2.0:” << endl; cout << “===================" << endl; – void, int, double, char, etc. cout << “ Enter an option:" << endl; cout << “ 1.) Start" << endl; – void means return nothing cout << “ 2.) Continue" << endl; cout << “ 3.) End \n" << endl; • Function name } bool only_2_3_factors(int num) – Any valid identifier { while(num % 2 == 0){ • Input arguments inside () ... } – Act like a locally declared ... if(num==1) variable return 1; return 0; • Code } – In {…} double triangle_area(double b, double h) { • Non-void functions must have double area = 0.5 * b * h; return area; 1 or more return statements } – First 'return' executed immediately quits function

7 Parameter Passing • Formal parameters, a and b #include <iostream> using namespace std; – Type of data they expect int max(int a, int b) Formals – Names that will be used internal to the function to { refer to the values (placeholders/aliases) for if(a > b) actuals return a; else • Actual parameters return b; – Actual values input to the function by the caller } – A copy is made and given to function int main() x { int x=6, z; Actuals 6 4 Actuals z = max(x,4); cout << “Max is “ << z << endl; Actuals z = max(125, 199); Formals a b 6 cout << “Max is “ << z << endl; return 0; max() } return val Each type is a "different" shape (int = triangle, double = square, char = circle). Only a value of that type can "fit" as a parameter..

8 Parameter Passing #include <iostream> • Formal parameters, n1 and n2 using namespace std; – Type of data they expect double avg(int n1, int n2) { – Names that will be used internal to the function to double sum = n1 + n2; refer to the values return sum/2.0; • Actual parameters } copy copy – Actual values input to the function code by the int main() caller { – A copy is made and given to function int x=6, y = 9; double z; x y z = avg(x,y); Actuals 6 9 cout << “AVG is “ << z << endl; z = avg(x, 2); cout << “AVG is “ << z << endl; Formals n1 n2 7.5 return 0; } avg() return val Each type is a "different" shape (int = triangle, double = square, char = circle). Only a value of that type can "fit" as a parameter..

9 Parameter Passing #include <iostream> • Formal parameters, n1 and n2 using namespace std; – Type of data they expect void inc(int x) { – Names that will be used internal to the function to x = x+1; refer to the values } • Actual parameters – Actual values input to the function code by the int main( ) caller { – A copy is made and given to function int x=6; x inc(x); 6 cout << “X is “ << x << endl; Actuals 6 return 0; } Formals x inc() x 7 Each type is a "different" shape (int = triangle, double = square, char = circle). Only a value of that type can "fit" as a parameter..

10 Example Functions 1 Function Signature/Prototype double calcInterest(double amt, int yrs, double rate); main #include <iostream> #include <cmath> using namespace std; 30 r amount // prototype double calcInterest (double amt, int yrs, double rate); int main() { double amount, r; cin >> amount >> r; double interest = calcInterest(amount, 30, r); amt yrs rate cout << "Interest: " << interest << endl; return 0; } interest calcInterest double calcInterest (double amt, int yrs, double rate) { return amt * pow(rate/12, 12*yrs); }

11 Example Functions 2 Function Signature/Prototype bool checkLogin(string exp_pwd); #include <iostream> main using namespace std; // prototype pass bool checkLogin (string exp_pwd); int main() { string pass = "Open123!"; // secret password bool valid; cout << "Enter your password: " << endl; valid = checkLogin(pass); exp_pwd if(valid == true) { cout << "Success!" << endl; } return 0; } valid checkLogin bool checkLogin (string exp_pwd) { string actual; cin >> actual; return actual == exp_pwd; }

12 Example Functions 3 Function Signature/Prototype void validateLogin(string exp_pwd); #include <iostream> main using namespace std; // prototype pass void validateLogin (string exp_pwd); int main() { string pass = "Open123!"; // secret password bool valid; cout << "Enter your password: " << endl; validateLogin(pass); exp_pwd return 0; } checkLogin void validateLogin (string exp_pwd) { string actual; cin >> actual; if(actual == exp_pwd){ cout << "Success!" << endl; } else { cout << "Incorrect!" << endl; } }

13 Example Functions 4 Function Signature/Prototype bool genCoinFlip(); #include <iostream> main #include <cstdlib> using namespace std; // prototype bool genCoinFlip (); int main() { bool heads; heads = genCoinFlip(); if(heads == true) { cout << "Heads!" << endl; } else { cout << "Tails!" << endl; } return 0; } heads genCoinFlip bool genCoinFlip () { int r = rand(); // Generate random integer return r%2; }

14 Program Decomposition • C is a procedural language – Main unit of code organization, problem decomposition, and abstraction is the “function” or “procedure” – Function or procedure is a unit of code that • Can be called from other locations in the program • Can be passed variable inputs (a.k.a. arguments or parameters) • Can return a value to the code that called it • C++ is considered an “object - oriented” language (really just adds objected-oriented constructs to C) – Main unit of organization, problem decomposition, and abstraction is an object (collection of code & associated data)

15 Exercise • To decompose a program into functions, try listing the verbs or tasks that are performed to solve the problem – Model a card game as a series of tasks/procedures… • shuffle(), deal(), cut(), drawCard(), checkIfWon (), … – A database representing a social network • addUser(), addFriend(), updateStatus(), etc.