While Loop problem using PIC12F683

[ahmedabosriaa]

Hi guys

I have a problem, hope to find help here

This is a simple program to let (B1= High) if (set = 8.1)
Unfortunately it doesn't work BUT it works only if we replaced the condition to (set<5.4 OR set<2.7).
So, could anyone tell me what is the problem.

double set;

void main() {

ANSEL =0b00100001;
GPIO=0;
TRISIO=0b000001; // All pins are output except pin one


while(1){
set=0;
while(set<8.1){
set+=2.7;
}
if(set == 8.1){
GPIO.B1 = 1;
}
}
}

 

[keith1200rs]

2.7 and 8.1 in binary are recurring numbers so rounding errors will make a genuine equals prone to problems.

Keith

 

[FvM]

I presume your code works according to C language specification. The problem is solely about understanding the nature of floating point numbers. Other than integer and fixed point numbers, they involve a rounding error. In the present case, matching 8.1 is missed by a very small difference. You can visualize by printing the numbers with full resolution.

But there's a simple solution: Never test for equality with float numbers, because it possibly never happens.

By the way, it seem pretty stupid to use float or even double (not actually supported by your compiler and casted to real, I guess) with a tiny PIC12F.

 

[Golden Electronics]

u may insert >=8.1 instead of set==8.1