Problem with calculating Percentage

[Dodu]

Hello everyone. I started learning C++ a few days ago. I have a problem. I am trying to calculate the percentage using the code below. But it's giving me a zero. I don't understand what I have done wrong. I have gone through the code many times.

#include <iostream>

using namespace std;

int main()
{
    int a = 10;  int b = 100;
    int per = (a/b) * 100;
    cout << "Percentage is : " << per << endl;
    return 0;
}

Shouldn't this code give me "Percentage is : 10"?
Would really appreciate it if someone would help. :)

[Akshit]

a/b=0.10 but as per is integer so it changes to 0.and 0*100 = 0.

Use

double per = (double)(a/b) * 100;

[Dodu]

Hey thanks ALOT! Does the double mean it's upto 2 decimal place or something?

[Akshit]

double is 8 byte in size and stores double the no of decimal places then float...um maybe about 16.You can use float instead of double to save memory.

int is 2 byte in size.

[Dodu]

Using this code, it still gives me 0. :/

#include <iostream>

using namespace std;

int main()
{
    int a = 10;  int b = 100;
    double per = (double)(a/b) * 100;
    cout << "Percentage is : " << per << endl;
    return 0;
}

[Peter87]

@Akshit
The byte sizes depends on the platform/compiler. int is at least 2 bytes but is nowadays often 4 bytes.

[Akshit]

I was talking about mostly used VC++.But yes you are true.

[Akshit]

@Dodu

My mistake.Use it like this

double per = ((double)a/(double)b) * 100;

or

float per = ((float)a/(float)b) * 100;

[Akshit]

or declare all variable as double or float.

[o3hC5Di1]

Just out of curiosity - wouldn't it suffice to cast just one of the two operands to double?
Won't the "lowest" type (int) be converted to the highest (float) if you do:

float per = static_cast<float>(a)/b*100

Just asking out of interest what the preferred way of doing this is :)

All the best,
NwN

[Peter87]

@NwN
Yes you are right. Only one cast is needed.

[Dodu]

@Akshit


Thank you! :)