# 2.2 Completing the basics  (Page 3/6)

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`<<setiosflags(ios::oct)<<15<<endl`

`<<"The hexadecimal (base 16) value of 15 is "`

`<<setiosflags(ios::hex)<<15<<endl;`

`return 0;`

`}`

The output of the above program:

The decimal (base 10) value of 15 is 15

The octal (base 8) value of 15 is 17

The hexadecimal (base 16) value of 15 is f

To designate an octal integer constant, the number must have a leading 0 . Hexadecimal number are denoted using a leading 0x .

Example

`// Octal and hexadecimal integer constant`

`#include<iostream.h>`

`int main()`

`{`

`cout<<"The decimal value of 025 is "<<025<<endl`

`<<"The decimal value of 0x37 is "<<0x37<<endl;`

`return 0;`

`}`

The output of the above program:

The decimal value of 025 is 21

The decimal value of 0x37 is 55

## Using mathematical library functions

Although addition, subtraction, multiplication and division are easily accomplished using C++’s arithmetic operators, no such operators exist for finding the square root of a number or determining trigonometric values. To facilitate such calculations, C++ provides standard library functions that can be included in a program.

Functions are normally called by writing the name of the function, followed by a left parenthesis, followed by the argument (or a comma-separated list of arguments) of the function, followed by a right parenthesis. For example, a programmer desiring to calculate and print the square root of 900.0 might write:

`cout<<sqrt(900.0);`

When this statement is executed, the math library function sqrt is called to calculate the square root of the number contained in the parentheses (900.0). The number 900.0 is the argument of the sqrt function. The preceding statement would print 30. The sqrt function takes an argument of type double and returns a result of type double.

If your program uses mathematic function sqrt(), it should have the preprocessor command #include<math.h> in the beginning of the program. This makes a mathematical library accessible. Below are some commonly used mathematical functions provided in C++.

Except abs(a), the functions all take an argument of type double and return a value of type double.

Example

`// this program calculates the area of a triangle`

`// given its three sides`

`#include<iostream.h>`

`#include<math.h>`

`int main()`

`{`

`double a,b,c, s;`

`a = 3;`

`b = 4;`

`c = 5;`

`s = (a+b+c)/2.0;`

`area = sqrt(s*(s-a)*(s-b)*(s-c));`

`cout<<"The area of the triangle = "<<area<<endl;`

`return 0;`

`}`

The output of the above program:

The area of the triangle = 6.0

## Casts

We have already seen the conversion of an operand’s data type within mixed-mode expressions and across assignment operators. In addition to these implicit data type conversions that are automatically made within mixed-mode expressions and assignment, C++ also provides for explicit user-specified type conversion. This method of type conversion is called casting . The word cast is used in the sense of “casting into a mold.”

Casting or type casting , copies the value contained in a variable of one data type into a variable of another data type.

The C++ syntax for casting variables is

`variable = new_type( old_variable);`

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