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Week 2.2 Predefined Libraries and Functions.pdf

Chapter 2: Using Pre-Defined

C++ Libraries and their

Functions

CSE 2010: Week 2

What this lecture

covers:

  • The cmath pre-defined C++ library
  • Using cmath functions

Pre-defined C++ Libraries

  • Background:
    • C++ library includes several pre-defined libraries that contain function that you can use in your code.
    • You have access to these libraries and can use them in your program with the #include statement #include
    • You can see a list of some here: http://www.cplusplus.com/reference/

Using Pre-defined Functions

  • Your main function (int main())is what controls the C++ program, but within main, you can call other functions to complete specific calculations or tasks.
  • Definition of Functions:
    • A function is a group of statements that perform a specific tasks.
  • By including pre-defined libraries, we have access to the functions within them. We cannot see the code for these functions, but we can still use them.
  • Syntax for using predefined functions:
    • functionName(parameters)
    • Each function has a unique name
    • Each function requires and accepts specific parameters. Parameters are the values that the function needs in order to return a specific value to you.
    • Each function returns up to a single value.
    • The number of parameters can vary on the function. Some have none, others have 2 or 3, etc.

- The C numerics library

http://www.cplusplus.com/reference/cmath/
  • To use functions in cmath, have the following line in your program, right after #include :
    • #include
  • Functions to compute trigonometry related calculations:
    • cos(x) //returns the cosine of the value x
    • sin(x) //returns the sine of the value x
    • tan(x) //returns the tangent of the value x
  • Exponential and logarithmic functions
    • log(x) //returns the log of x
    • log2(x) // returns the log base 2 of x
  • Power functions:
    • pow(x,n) // returns the value x raised to the n
    • sqrt(x) //returns the square root of x
  • You can use these functions anywhere that you would use a regular value
    • cout statement
    • variable definition
    • arithmetic expressions
    • as the parameter for another function call

Program example of using pow(), where the function call is used in two different ways, but we would get the same output #include #include using namespace std; int main() { //function call as part of a cout statement int a = 7, b = 3; cout << a << “ raised to the power of “ << b << “ is: “ << pow(a,b) <<“\n”; //function call as part of a variable definition int value = pow(a,b); cout << a << “ raised to the power of “ << b << “ is: “ << value << “\n”; return 0; } Output of program above: 7 raised to the power of 3 is 343 7 raised to the power of 3 is 343

Things to remember when converting mathematical expressions to valid C++ expressions

  • You are limited to characters that are on your keyboard
    • No square root symbol
    • No log
    • No exponents or subscripts
  • Before you implement the statement in your program, make sure you have all the necessary variables/values
    • If your formula/expression uses specific variables, be sure that they have been declared.
  • Include all necessary libraries
  • Let’s try an example with the quadratic formula!