c++ - floating point values comparison failure

In C, if we execute the following code:

float a = 0.7;
if (a < 0.7)
{
    printf("Less");

}
else
{
    printf("no");
}

The code above code prints "Less".

But if we execute the following code:

float a = 1.7;
if (a < 1.7)
{
    printf("Less");
}
else
{
    printf("no");
} 

It prints "no".

What's the reason for that? How does the float datatype work?