sqrt, sqrtl and sqrtf in C++

The cmath header defines two more inbuilt functions for calculating square root of a number (apart from sqrt which takes double as an arguement) which has an arguement of type float and long double.

1. double sqrt(double arg): It returns the square root of a number to type double

   Syntax : double sqrt(double arg)
   

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   // CPP code to illustrate // the use of sqrt function. #include <cmath> #include <iomanip> #include <iostream>    using namespace std;    int main() {     double val1 = 225.0;     double val2 = 300.0;        cout << fixed << setprecision(12) << sqrt(val1) << endl;     cout << fixed << setprecision(12) << sqrt(val2) << endl;        return (0); }

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   Output:

   15.000000000000
   17.320508075689
   

   Errors and exceptions associated with this function:
   (Thanks to sunny6041 for contributing this section)

   1. It is mandatory to give both the arguments otherwise it will give error no matching function for call to ‘sqrt()’ like this.
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      #include <iostream> #include <cmath> using namespace std;    int main() {     double answer;                answer = sqrt();     cout << "Square root of " << a           << " is " << answer << endl;        return 0; }

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      Output:

      prog.cpp:9:16: error: no matching function for call to 'sqrt()'
      

   2. If we pass a negative value in the argument domain error occurs. and the output will be the Square root of -a is -nan.
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      #include <iostream> #include <cmath> using namespace std;    int main() {     double a = -2 ,  answer;                answer = sqrt(a);     cout << "Square root of " << a           << " is " << answer << endl;        return 0; }

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      Output:

      Square root of -2 is -nan
      
      

2. float sqrtf(float arg): It returns the square root of a number to type float

   Syntax : float sqrtf(float arg)
   

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   // CPP code to illustrate // the use of sqrtf function. #include <cmath> #include <iomanip> #include <iostream>    using namespace std;    int main() {     float val1 = 225.0;     float val2 = 300.0;        cout << fixed << setprecision(12) << sqrtf(val1) << endl;     cout << fixed << setprecision(12) << sqrtf(val2) << endl;        return (0); }

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   Output:

   15.000000000000
   17.320508956909
   

3. long double sqrtl(long double arg): It returns the square root of a number to type long double with more precision. Advantage of using this function is that when working with integers of the order 10¹⁸, calculating its square root with sqrt function may give an incorrect answer due to precision errors as default functions in programming language works with floats/doubles. But this will always give an accurate answer.

   Syntax : long double sqrtl(long double arg)
   

   An illustration given below shows the exact difference when working with long integers with sqrt and sqrtl.
   Using sqrt function.

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   // CPP code to illustrate // the incorrectness of sqrt function. #include <cmath> #include <iomanip> #include <iostream>    using namespace std;    int main() {     long long int val1 = 1000000000000000000;     long long int val2 = 999999999999999999;        cout << fixed << setprecision(12) << sqrt(val1) << endl;     cout << fixed << setprecision(12) << sqrt(val2) << endl;        return (0); }

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   Output:

   1000000000.000000000000
   1000000000.000000000000
   

   Output:

   1000000000.000000000000
   1000000000.000000000000
   

   Using sqrtl function

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   // CPP code to illustrate // the correctness of sqrtl function. #include <cmath> #include <iomanip> #include <iostream>    using namespace std;    int main() {     long long int val1 = 1000000000000000000;     long long int val2 = 999999999999999999;        cout << fixed << setprecision(12) << sqrtl(val1) << endl;     cout << fixed << setprecision(12) << sqrtl(val2) << endl;        return (0); }

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   Output:

   1000000000.000000000000
   999999999.999999999476
   

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