Prewritten Functions

C++ doesn't offer many built in keywords or functions, and that's alright because with many compilers comes standard header files. These header files contain functions that we can use to enhance our programs and not write new functions. To call a function we either use an output statement or store it in a variable. We put the function name and then enter parenthases and put in the required parameters. A parameter is what is being passed down to the function. Assuming we already initialized the variables and have the proper heading file, to call the pow function and put into a variable x would be:

x=pow(2.0, 9)


The pow will take the 2.0 and put it to the 9th power. Below is a table which lists some useful functions, the type of parameters, and which header file they're in.
Function Header File Purpose Parameter(s) Type Result
abs(x) cmath Returns the absolute value int (some compilers like .NET 2005 will allow other numerical data) int (unless other numerical data was accepted)
sin(x) cmath Returns the sine double double
cos(x) cmath Returns the cosine double double
tan(x) cmath Returns the tangent double double
pow(x, y) cmath Returns x to the yth power double double
sqrt(x) cmath Returns square root of x float float
toupper(x) cctype Returns the uppercase of a char char char
tolower(x) cctype Returns the lowercase of a char char char
clock() ctime Returns CPU time taken for the program to run double
strcmp(x, y) string Returns int < 0 when y is < x, 0 when x and y are equal and int > 0 when x > y string, string int
char(x) Returns a character int char
double(x) Returns a double int double
rand() Returns a random number double


There are many more prewritten functions that come with the compilers, and many more that you can download from the web. I have just listed what I feel are the most useful prewritten functions. In the next section you'll learn how to write your own.

Next Section: Writing Your Own Functions
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