This question already has answers here:
How do I print a double value with full precision using cout?
(17 answers)
Closed 7 years ago.
I have tried to use long double type in my program to print out more digits of pi. But it only shows 5 digits decimal.
Here is my code.
int main(int argc, char** argv) {
long double pi_18 = acos(static_cast<long double>(-1));
cout << "pi to 18:" << pi_18 << endl;
return 0;
}
and this is my output:
pi to 18: 3.14159
How can I fix this problem?
Like so:
#include <iomanip>
#include <iostream>
std::cout << std::setw(15) << pi_18 << std::endl;
The width modifier only affects the next formatting operation, so if you want to format multiple numbers, you have to repeat it before every one. Check out the full documentation of format specifiers.
You could use the precision method:
cout.precision(15);
This allows you to define the precision only once. You don't have to repeat it like with std::setw()
For more information see:
http://en.cppreference.com/w/cpp/io/ios_base/precision
Related
This question already has answers here:
How to specify setprecision rounding
(4 answers)
Closed 1 year ago.
I'm doing my ICT homework and I ran into this problem: the decimals keep on getting rounded off when I print them. I've already included the <iomanip> header and used the fixed and setprecision manipulators, but it still keeps getting rounded off. Here's my code:
#include <iostream>
#include <iomanip>
using namespace std;
int main ()
{
double num1 = 3.12345678
cout << fixed << setprecision (4);
cout << num1 << endl;
return 0;
}
When I run the program, "3.1235" comes out instead of "3.1234," which is the expected output according to my teacher. How do I prevent the fourth decimal from rounding off?
Expanding answer of #eerorika. You can use std::fesetround() to set rounding strategy, as in code below. It outputs 3.1234 as you wished. Possible values for this function's argument are FE_DOWNWARD, FE_TONEAREST, FE_TOWARDZERO, FE_UPWARD.
Try it online!
#include <iostream>
#include <iomanip>
#include <cfenv>
int main() {
double num = 3.12345678;
std::fesetround(FE_TOWARDZERO);
std::cout << std::fixed << std::setprecision(4) << num << std::endl;
}
Output:
3.1234
3.1234 is not the expected output, setprecision will round to the specified precision.
One solution to get 3.1234 is to round to the desired number of decimal places yourself (std::trunc just rounds towards zero):
#include <cmath>
...
std::cout << std::fixed << std::setprecision(4);
std::cout << std::trunc(num1 * 10000) / 10000 << endl;
If you want to prevent rounding i.e. you want to see more precision, you can use a higher value with setprecision.
If you want to round towards zero instead of rounding towards nearest, you can use the FE_TOWARDZERO rounding mode.
This question already has answers here:
Floating point format for std::ostream
(8 answers)
Closed 8 years ago.
my problem is when I am trying to print a floating-point GPA in C++.
It seems like a simple issue, but I can't get it to work. Basically I have a floating point value set to 4.0 for a GPA. However, when I try to print it like this:
cout << gpa << endl;
I get the value of 4. Without the .0 on the end. However, I want the .0 to show up. I have tried setting a precision but with no luck. Any help is appreciated.
You can use std::fixed in conjunction with std::setprecision
#include <iostream> // std::fixed
#include <iomanip> // std::setprecision
int main() {
double gpa = 4.0;
std::cout << std::fixed << std::setprecision(1) << gpa << std::endl;
return 0;
}
// Output is 4.0
#include <iomanip>
...
cout.setf(ios::fixed); // use fixed-point notation
cout.setf(ios::showpoint); // show decimal point
cout.precision(1);
...
cout << gpa << endl;
This question already has answers here:
Round double to 3 points decimal [duplicate]
(4 answers)
Closed 4 years ago.
I've used the following to round my values to 2 decimal points:
x = floor(num*100+0.5)/100;
and this seems to work fine; except for values like "16.60", which is "16.6".
I want to output this value like "16.60".
The way I'm outputting values is the following:
cout setw(12) << round(payment);
I've tried the following:
cout setw(12) << setprecision(2) << round(payment);
But that gave me answers like
1.2e+02
How can I output the values correctly?
This is because std::setprecision doesn't set the digits after the decimal point but the significant digits if you don't change the floating point format to use a fixed number of digits after the decimal point. To change the format, you have to put std::fixed into your output stream:
double a = 16.6;
std::cout << std::fixed << std::setprecision(2) << a << std::endl;
you can use printf / sprintf or other similar functions. Following code will format floating point value into two digits after decimals. Refer to the printf manual for more formatting info
float f = 1.234567
printf("%.2f\n", f);
From Trevor Boyd Smith's comment:
If you are allergic to printf and friends there is the type safe C++ version in #include <boost/format.hpp> which you can use to do:
float f = 1.234567;
cout << boost::format("%.2f") % f << endl;
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
floating point precision
when I do cout<<8.0 .Its getting printed as 8.How to Print in the output console of c++ the entire zeros after decimal point like 8.00000000
I tried this cout<<setprecision(5)<<(double)8.0; still printing 8
Use the fixed manipulator
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
cout << fixed << setprecision(6) << (double)8 << "\n";
return 0;
}
http://ideone.com/ShcNIc
See How do I print a double value with full precision using cout?
cout.precision(15);
cout << fixed << 8.0;
This question already has answers here:
How do I print a double value with full precision using cout?
(17 answers)
Closed 6 years ago.
I want to output the value of a double in it's full precision. However, when using the cout function, it only displays the first 6 digits even though there is around 15-16 digits of precision.
How do I get my program to display the entire value, including the magnitude (power) component?
Use the setprecision() manipulator:
http://www.cplusplus.com/reference/iostream/manipulators/setprecision/
You can also force scientific notation with the scientific manipulator:
http://www.cplusplus.com/reference/iostream/manipulators/scientific/
cout << scientific << setprecision(15) << my_number << endl;
you could use something like this :
#include <iomanip>
cout << setprecision (9) << double_value << endl;
more iomanipulators, here
You're looking for setprecision (code taken from link):
int main () {
double f =3.14159;
cout << setprecision(15) << f << endl;
return 0;
}