In C++, we can use the **`atof()`** function to convert a string to a floating-point value of datatype `double`. This function interprets the contents of the string as a floating-point number.

# Library
To use the `atof()` function, include the following library:
```C
#include <cstdlib>
```
# Declaration
The `atof()` function can be declared as follows:
```C
double atof(const char* str);
```
* `str`: The string that is converted to a floating-point number.

# Return value
The `atof()` function returns a `double` type variable that is the floating-point interpretation of the string `str`.

>The `atof()` function returns `0` if :
>* `str` is empty.
>* `str` contains only whitespace characters.
>* The sequence of non-whitespace characters in `str` is not a valid floating-point number.

# Code
## Example 1
Consider the code snippet below, which demonstrates the use of the `atof()` function with different string inputs.


#include <cstdlib>
#include <iostream>
using namespace std;

int main()
{
	
	char str1[] = "123.12"; 
	char str2[] = "-123.7"; 
	char str3[] = "12.6end with words";
	char str4[] = "start with words12.0";

	double asint1 = atof(str1); 
	cout << "atof(" << str1 << ") = " << asint1 << endl;

	double asint2 = atof(str2); 
	cout << "atof(" << str2 << ") = " << asint2 << endl;

	double asint3 = atof(str3); 
	cout << "atof(" << str3 << ") = " << asint3 << endl;

	double asint4 = atof(str4); 
	cout << "atof(" << str4 << ") = " << asint4 << endl;
	
	return 0;
}


## Explanation
Four strings, `str1`, `str2`, `str3`, and `str4`, are declared in *lines 8-11*. We use the `atof()` function in *line 13*, *line 16*, *line 19*, and *line 22* to convert `str1`, `str2`, `str3`, and `str4` to floating point numbers.

## Example 2
Consider to code snippet below, which demonstrates the case when the `atof()` function returns `0`.

#include <cstdlib>
#include <iostream>
using namespace std;

int main()
{
	
	char str1[] = ""; 
	char str2[] = " \t "; 
	char str3[] = "abc"; 

	double asint1 = atof(str1); 
	cout << "atof("<< str1 <<") = " << asint1 << endl;

	double asint2 = atof(str2); 
	cout << "atof(" << str2 << ") = " << asint2 << endl;

    double asint3 = atof(str3); 
	cout << "atof(" << str3 << ") = " << asint3 << endl;
	
	return 0;
}

## Explanation
Three strings, `str1`, `str2`, and `str3`, are declared in *lines 8-10*.
* *line 12*: We use the `atof()` function to convert `str1` to a floating-point number. The `atof()` function returns `0`, as `str1` is empty.
* *line 15*: We use the `atof()` function to convert `str2` to a floating-point number. The `atof()` function returns `0`, as `str2` only contains whitespace characters.
* *line 18*: We use the `atof()` function to convert `str3` to a floating-point number. The `atof()` function returns `0`, as non-whitespace characters of `str3` do not represent a valid-floating point number.

What is atof() in C++?

Library

Declaration

Return value

Code

Example 1

Explanation

Example 2

Explanation