# Function part 3 (built in functions)

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Built-in functions in C++ are functions that are provided by the compiler and are available to use in any C++ program. These functions are typically used for common tasks such as input/output, mathematical operations, and string manipulation.

ere are some of the most common built-in functions in C++:

• Mathematical functions:
• `abs()`: Returns the absolute value of a number.
• `sqrt()`: Calculates the square root of a number.
• `pow()`: Raises a number to a power.
• `sin()`: Calculates the sine of an angle in radians.
• `cos()`: Calculates the cosine of an angle in radians.
• `tan()`: Calculates the tangent of an angle in radians.
• `floor()`: Returns the greatest integer less than or equal to a number.
• `ceil()`: Returns the smallest integer greater than or equal to a number.
• String manipulation functions:
• `strlen()`: Returns the length of a string.
• `strcpy()`: Copies one string to another string.
• `strcat()`: Concatenates two strings.
• `strcmp()`: Compares two strings and returns an integer value indicating whether they are equal, less than, or greater than each other.
• Input/output functions:
• `cin`: Reads data from the standard input stream.
• `cout`: Writes data to the standard output stream.
• `cerr`: Writes data to the standard error stream.
• `fopen()`: Opens a file for reading or writing.
• `fclose()`: Closes a file.

Example 1:

`cout << sqrt(18) << endl;`

Output:

`4.24264`

Example 2:

`cout << abs(-18) << endl;`

Output:

`18`

Example 3:

`cout << mod(10.5,2) << endl;`

Output:

`0.5`

Example 4:

`cout << floor(10.2) << endl;`

Output:

`10`

Example 5:

`cout << floor(-10.2) << endl;`

Output:

`-11`

Example 6:

`cout << ceil(10.2) << endl;`

Output:

`11`

Example 6:

```#include <iostream>

using namespace std;

int main()
{
cout << sqrt(abs(pow(-3,2))) << endl;

return 0;
}```

To use a built-in function, you simply need to include the appropriate header file. So you might have a problem executing this program. you would need to include the `<cmath>` header file.

The `<cmath>` header file contains declarations for a number of mathematical functions, such as `sqrt()`, `pow()`, `sin()`, `cos()`, and `tan()`. These functions are useful for performing common mathematical operations, such as calculating the square root of a number, raising a number to a power

```#include <iostream>
#include <cmath>
using namespace std;

int main()
{
cout << sqrt(abs(pow(-3,2))) << endl;

return 0;
}```

Output:

`3`

Example 7:

```#include <iostream>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
cout << max(10,5) << endl;

return 0;
}```

You would need to include the `<algorithm>` header file to use any of the algorithms provided by the C++ standard library. These algorithms include sorting, searching, merging, and many more.

Output:

`10`

Example 8:

```#include <iostream>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{
cout << max(15,max(10,5)) << endl;

return 0;
}
```

Output:

`15`

Example 9:

```#include <iostream>
#include <algorithm>
#include <cmath>

using namespace std;

int main()
{

int x = 0, y = 10;
swap(x,y);
cout << "x= " << x << "y= " << y << endl;

return 0;
}
```

Output:

```x= 10y= 0
```

Built-in functions can be a very useful tool for C++ programmers. By using built-in functions, you can avoid having to write your own code for common tasks.