sqrt, sqrtl and sqrtf in C++

Last Updated : 04 Nov, 2019

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

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

Syntax : double sqrt(double arg)

// 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); 
} 

Output:

15.000000000000
17.320508075689

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

It is mandatory to give both the arguments otherwise it will give error no matching function for call to ‘sqrt()’ like this.

#include <iostream> 
#include <cmath> 
using namespace std; 
  
int main() 
{ 
    double answer; 
          
    answer = sqrt(); 
    cout << "Square root of " << a  
         << " is " << answer << endl; 
  
    return 0; 
} 

Output:

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

If we pass a negative value in the argument domain error occurs. and the output will be the Square root of -a is -nan.

#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; 
} 

Output:

Square root of -2 is -nan

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

Syntax : float sqrtf(float arg)

// 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); 
} 

Output:

15.000000000000
17.320508956909

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.

// 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); 
} 

Output:

1000000000.000000000000
1000000000.000000000000

Output:

1000000000.000000000000
1000000000.000000000000

Using sqrtl function

// 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); 
} 

Output:

1000000000.000000000000
999999999.999999999476

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