CS 105 Lecture 10
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CS 105 Lecture 10 Functions. Version of Mon, Mar 28, 2011, 3:13 pm. Quiz 2 Scores. Hmm. 17 Scores: 474338 3734 32 3229 2722 22 21 2114109 9 Avg 26.3/50 (or 52.6/100)Std dev 11.7. Quiz 2 Scores. Numerous problems came from Labs. Functions.

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CS 105 Lecture 10 Functions

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Cs 105 lecture 10 functions

CS 105 Lecture 10

Functions

Version of Mon, Mar 28, 2011, 3:13 pm


Quiz 2 scores

Quiz 2 Scores

  • Hmm....

17 Scores:

474338 3734 32 3229 2722 22 21 2114109 9

Avg 26.3/50 (or 52.6/100)Std dev 11.7


Quiz 2 scores1

Quiz 2 Scores

  • Numerous problems came from Labs


Functions

Functions

  • Function: A discrete piece of code that performs a specific operation or task

  • Named with a descriptive identifier

  • Called from main() or another function

  • When called, program control (execution) is transferred to the function.

  • Function performs required tasks, and then possibly returns a value.

  • After return from function, control returns to the statement following the function call.


Function attributes

Function Attributes

  • Function Name: Identifier used to call function.

  • Function Parameter(s) or Argument(s): value(s) passed into function for use by function code.

  • Function Return Value: Value returned by function back to calling function.


Math library

Math Library

  • Provides a library of common math functions. Get via #include<cmath>

  • Must call functions with correct number and order of parameters.

  • Functions return value after calculations.

  • Example: The power function pow; square root function sqrt.

  • double bigValue;

  • double base = 2.0, exponent = 20.0;

  • bigValue = pow(base, exponent);

  • cout << bigValue << " " << sqrt(bigValue) << endl;


User defined functions

User-Defined Functions

  • We can write our own functions; we need to specify the name of the function, the number and kinds of parameters it takes, and the kind of value it returns (if any).

    • Plus, the "body" of the function — the code that does the calculation

  • Example:

  • double calcAverage(int total, int numItems)

  • {

  • double result = (double) total / numItems;

  • return result;

  • }


Define function before main

Define Function Before Main

  • #include <iostream>

  • using namespace std;

  • double calcAverage(int total, int numItems)

  • {

  • double result = (double) total / numItems;

  • return result;

  • }

  • int main()

  • {

  • int sumGrades = 921, numStudents = 10;

  • double avgGrade;

  • avgGrade = calcAverage(sumGrades,numStudents);

  • cout << avgGrade << endl;

  • cout << calcAverage(1200, 14) << endl;

  • }


Define functions after main

Define Functions After Main?

  • If you have many functions, then you might have a lot of code to get through before you actually get to the main program.

  • Nice to have the main program first and the functions afterward.

    • But what if we use calcAvg before we give its definition?

    • How will the compiler know if we're calling calcAvg correctly?


Use function prototype

Use Function Prototype

  • A function prototype tells the compiler how we'll use the function. (Omits the function body.)

  • #include <iostream>

  • using namespace std;

  • Function Prototype "declares" calcAverage

  • double calcAverage(int total, int numItems); ←–––––– NOTE !

  • int main()

  • {

  • // etc

  • }

  • "Definition" of calcAverage gives its body

  • double calcAverage(int total, int numItems)

  • {

  • // rest of body as before

  • }


Declaring a function

Declaring a Function

  • Function Prototype: Declares a function's name and how it is called; it doesn't define the body of the function.

  • Used by the compiler check for syntax errors in how we call the function

  • Example:

  • double calcAverage(int total, int numItems);

    • double is the return type.

    • calcAverage is the function name.

    • total is the first parameter and it has type int

    • numItems is the second parameter and it has type int.

  • Standard functions (e.g., those in the STL = Standard Template Library) have function prototypes in header files that we #include.


Functions return types

Functions – Return Types

  • A function with a return type of int must have a return of some integer.

    • Similarly, a function with a return type of double must have a return of some double, etc.

    • That's why main programs include return0;

  • A function with void as its return type doesn't return a value. (A.k.a. "void" function)

    • It can have a return; statement (with no value).

    • Or it can fall off the end of the function (a return; is assumed).


Parameters arguments

Parameters & Arguments

  • May pass as many parameters as necessary to function.

  • A copy of the value of the parameter is passed to the function.

  • Changing the value of the parameter in the function does not affect the value of the original variable.

  • This is called Pass-by-Value


Example of void function

Example of void function

  • #include <iostream>

  • using namespace std;

  • void printNum(int); // function prototype

  • int main()

  • {

  • int myNumber = 7;

  • printNum(myNumber); // function call

  • printNum(9);

  • return 0;

  • }

  • // begin function definition

  • void printNum(int numToPrint)

  • {

  • cout << numToPrint;

  • }


Functions1

Functions

  • Write a function that accepts one integer as a parameter. The function returns the sum of the integers from 1 to the integer passed to the function.

  • 5 minutes …… GO!


Sum function

Sum Function

  • int sumOfInt(int num)

  • {

  • int i, sum = 0;

  • for(i = 1; i <= num; i++)

  • sum = sum + i;

  • return(sum);

  • }


Function calls

Function Calls

  • Write a function call to call sumOfInt with an argument of 5, save the return value into a variable and print it out.

  • 2 minutes – GO!


Function calls1

Function Calls

  • int sumOfInt(int);

  • int main()

  • {

  • int sum5;

  • sum5 = sumOfInt(5); cout << sum5 << endl;

  • return 0;

  • }


Display line function

Display Line Function

  • Write a function that displays a character some number of times to the display. The function is passed the character and the number of times to display it.

  • 5 minutes: GO!


Displaychar function

displayChar() Function

  • void displayChar(char charPassed, int times)

  • {

  • int i;

  • for(i = 0; i < times; i++)

  • cout << charPassed;

  • cout << endl;

  • }


Cs 105 lecture 10 functions

  • do

  • {

  • theLabs(threeHoursAWeek);

  • }

  • while (!semesterDone);


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