rint(), rintf(), rintl() in C++

rint() is used to round of the floating-point argument to an integer value (in floating-point format). You can also determine the current rounding mode using a function fesetround() according to which the rint function returns the rounded integer value.

Syntax
double rint(double x);
float rint(float x);
long double rint(long double x);

Header file :  cmath
Parameters :  The rint() function takes a single 
argument value to round.

Returns :   By default, the rounding direction is set to 
'to-nearest' otherwise the rint() function rounds the argument 
to an integral value, using the rounding direction 
specified by fegetround() and returns the value.

Exceptions or Errors
1. If the result of the function is outside the range of the return type, a domain error error may occur.
2. If the argument is 0, it is returned unmodified.
3. If the argument is infinite, it is returned unmodified.

Examples:

Input : 3.3
Output : 3

Input : 3.5
Output : 4

Input : 3.7
Output : 4
// CPP program to illustrate rint()
#include <cmath>
#include <iostream>
using namespace std;
// Driver Program
int main()
{
    double a, b, x = 3.3, y = 3.7;

    // Saves the rounded value to a variable
    a = rint(x);
    b = rint(y);

    // Prints the rounded value
    cout << a << endl;

    cout << b;
    return 0;
}

Output:

3
4

fesetround() function



By default, the rounding direction is set to the nearest integer. But using fesetround() function, we can the direction of our choice.
Syntax :

fesetround(FE_DOWNWARD)
fesetround(FE_UPWARD)
Header file : cfenv

Example :

  • If rint() function is used with argument 3.7 and fesetround(FE_DOWNWARD) is also used, the output would be 3
  • If rint() function is used with argument 3.3 and fesetround(FE_UPWARD) is also used, the output would be 4
// CPP program to illustrate rint()
// with fesetround() function
#include <cfenv>
#include <cmath>
#include <iostream>
using namespace std;
// Driver Program
int main()
{
    double x = 3.7, y = 3.3, result;

    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);

    result = rint(x);
    cout << result << endl;

    // setting rounding direction to UPWARD
    fesetround(FE_UPWARD);

    result = rint(y);
    cout << result << endl;

    return 0;
}

Output:

3
4

rintf() function

rintf() function is same as the rint function. The only difference is that the parameter and return type of the function is float type. The ‘f‘ character appended to ‘rintf‘ stands for float and it signify the parameter type and return type of the function.

Syntax :
float rintf(float x);

Here, variables are assigned float type otherwise type mismatch error occurs.

// CPP program to illustrate rinft()
#include <cfenv>
#include <cmath>
#include <iostream>
using namespace std;
// Driver Program
int main()
{
    float x = 3.76542, y = 3.37562, result;
    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);

    result = rintf(x);
    cout << result << endl;

    // setting rounding direction to UPWARD
    fesetround(FE_UPWARD);

    result = rintf(y);
    cout << result << endl;

    return 0;
}

Output:

3
4

rintl() function

rintl() function is same as the rint function.The only difference is that the parameter and return type of the function is long double type.The ‘l‘ character appended to ‘rintl‘ stands for long double and it signify the parameter type and return type of the function.

Syntax : 
long double rintl(long double x);

Here, variables are assigned long double type otherwise type mismatch error occurs.

// CPP program to illustrate rinfl()

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

// Driver Program
int main()
{
    long double x = 3.765426764, y = 3.37562657, result;

    // setting rounding direction to DOWNWARD
    fesetround(FE_DOWNWARD);

    result = rintl(x);
    cout << result << endl;

    // setting rounding direction to UPWARD
    fesetround(FE_UPWARD);

    result = rintl(y);
    cout << result << endl;

    return 0;
}

Output:

3
4




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