While Loop problem using PIC12F683

ahmedabosriaa · Jun 27, 2013

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 · Jun 27, 2013

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

Keith

FvM · Jun 27, 2013

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 · Jun 27, 2013

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

While Loop problem using PIC12F683

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While Loop problem using PIC12F683

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