C++ weird thing

Question

Hi there, anyone can explain me, why this parts of code are acting differently?

while((c = fread(buf, sizeof(char), 1, f)) != 0);
{
    if(write(t, buf, c) < 0)
    {
        return E_MSGSEND;
    }
}

/////////////////////////////////////

do
{
    c = fread(buf, sizeof(char), 1, f);
    if(write(t, buf, c) < 0) 
    {
            return E_MSGSEND;
    }
} while(c != 0);

while {} runs only 1time but do {} while 5times. Whats is the difference? Before while {} c is intialized to 1.

Thanks an advice

Answer 1

You have a semicolon after your first while:

while((c = fread(buf, sizeof(char), 1, f)) != 0);

This in effect makes it an empty loop, which may well execute the same amount of times as the other loop, but its body doesn't include any statements. The following if, though, is not part of that loop anymore, so it only executes once.

Answer 2

In the first section, using the while loop, you check for EOF or successful read before executing the inner statements.

In the second section, using the do-while loop, you don't check for EOF before executing the if statement.