for循环条件始终为true

Question

I have a For loop in C:

u8 i;
for (i=0; i <= 255; i++)
{
    //code
}

Now the compiler complains that "comparison is always true due to limited range of data type" I understand that 255 is u8 max but a for loop must have a condition. What should I put there then? Thanks.

Answer 1

uint8_t i=0;
do {
    //code
}while(++i);

Answer 2

what is u8 ? if it means 8-bit unsigned int, then 255+1 gives zero again, so the loop starts over again. you should use larger integer type. or use do-while as suggested in replies

Answer 3

u8 i=0,iold;
do{
    //code
    iold=i++;
}while(iold<i);

Answer 4

u8 someFunction()
{
    int i;
    for (i = 0; i < 256; i++)
    {
        // do something with i here and /or break
    }

    if (i == 256)
    {
        // loop ran completely without a break
    }

    return i; // will convert i to "u8" type (256 will become 0)
}

Answer 5

A for loop doesn't necessarily need a condition. If you want the loop to not have any condition at all, you can write:

for (i = 0; 1 ; i++)

or

for (i = 0; ; i++)

But beware that i will overflow after reaching 255, and start over back from zero each time.

If you don't want it to loop infinitely, then either place a break; somewhere inside the loop, or use an appropriate condition inside the condition field of the for loop.

And to be honest, I am not sure why your compiler is even complaining about a condition being always true...

Answer 6

What should I put there then?

Use a larger type like int type.