Get percent of number in c++

Question

How can I calculate several percent of int?
for example I want to get 30% from number, if I will use this example of code, I will get wrong answer:

int number = 250;
int result = (number / 100) * 30;  

result will be 60, and the real answer is 75, is there any way to calculate it?

Answer 1

Multiply before dividing:

int result = number * 30 / 100;

The reason you get the result you get is that division with integer types produces an integer result: 250 / 100 is 2. If you multiply before dividing you still get an integer result, but at least you haven't lost data in intermediate steps. If you have to deal with really huge numbers there is a danger of overflowing the range permitted by int though.

Alternatively you can use floating point arithmetic, where division can produce fractions of integers:

int result = number * 0.30;

This may produce unexpected results though, so you're better off using integers only as above. Or write 3.0/10 instead of 0.30.

Answer 2

Assuming the numbers are small(ish), you can just turn it around:

 int result = (number * 30) / 100;

(Parenthesis not required, but helps clarify).

This won't work if either of the numbers are several million, but should be fine for numbers smaller than that.

Answer 3

Switching the operands (as others suggested) would work too, but just in case you do not want to, there's another solution:

int number = 250;
int result = static_cast<double>(number) / 100 * 30; 

Answer 4

Try this,

int number = 250;
float result = number  * (float)(30/100.0);

Answer 5

Another possibility, good in Windows when working with 32 bit numbers.

int num = 750;

int result;

result = MulDiv( num, 30, 100 );

https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-muldiv

Answer 6

You need to perform floating point math, otherwise the compiler does all the arithmetic here as integers.

You might try

int result = (number / 100.0) * 30;

Answer 7

Use float:

float number = 250;
float result = (number / 100.0) * 30

Also just putting there the 100.0 with deciaml point might be enough.

Because if you do it your way 250 / 100 in integer equals 20( you can put 100 in 200 only twice and integer doesn't care about the rest 50) and times 30 = 60.

Answer 8

Now I think about some solution:

int number = 250;
int result = number * 100;
result = (result / 100) * 30;
result /= 100;

Answer 9

The whole program is like:

double number , result;

cout << "Enter the number:";
cin >> number;

result = number * 30.0 / 100;
cout << "Result = " << result << endl;

and you will get your answer....

Answer 10

score/items*30 ex;

15%

int score, items;
cout<<"input your score"<< score<<endl;
cin>>score;
cout<<"input number of items"<<items<<endl;
cin>>items;
float total=score/items*15
cout<<"you got "<<total<<""<<endl;

Answer 11

This is a First-degree equation, simpler than it looks!

float annualGrossSalary;
cout << "Please enter your annual salary: ";
cin >> annualGrossSalary;
float annualNetSalary = (annualGrossSalary - (annualGrossSalary / 100) * 40);
float monthyGrossSalary = annualGrossSalary / 12;
float monthyNetSalary = annualNetSalary / 12;
cout << "Your monthly gross salary is " << monthyGrossSalary << "\n";
cout << "Your monthly net salary is " << monthyNetSalary << "\n";
cout << "In 10 years you will earn " << annualNetSalary * 10 << "\n";