如何从输入C ++分别读取整数和分数

Question

My doubt is to skip a " . " from the input stream and read the whole number and the fractional parts in two different variables. Say I have an input like 10.26, I want store 10 in one variable a and 26 in another variable b .

In C , using scanf , I will do it like

scanf("%d.%d",&a,&b);

What is the equivalent way to do in C++ using cin ? or should I include cstdio and use the scanf itself?

Answer 1

You can read the float as normal and use C-library's modf function to split the number:

#include <cmath>

float f = 0.0;
float ipart = 0.0;
float fpart = 0.0;

if (cin >> f)
    fpart = modf(f, &ipart);
else {
    // input failed
}

Let operator>> do the error checking!

Answer 2

You can still use scanf in C++. If you want to use cin , then you can use ignore to skip over the . in the input. Read the integers into variables as usual:

cin >> a;
cin.ignore(1, '.');
cin >> b;

Beware that whatever you use, you lose information about the fractional part. Whether the value is .1 or .001 , you'll find b == 1 when you're finished. They're very different values, though.

Answer 3

Here's one way:

int egral;
unsigned int frac;
char sep;

if (!(std::cin >> egral >> sep >> frac) || sep != '.')
{
    // error, could not parse number
}

// integral part is 'egral, fractional part in 'frac'

Note that this would (wrongly?) parse 1.5E2 as 1 + 0.5 , and not as 150 + 0 . You'd have to add extra logic to handle scientific notation situations. It might be simpler to read an actual float and use modf .