# Howto compare floating point numbers in the C programming language

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### Description Edit

It is very usual for the C programming language beginners to compare a floating point number using the "==" operator. Floating point numbers must not be compared with the "==" operator.

That is mainly because when you compute a float number you will get a result like 1.543645274878272 and if you compare 1.543645274878272 with 1.5436, the result will always be false.

1.543645274878272 != 1.5436

### Solution using a function Edit

Instead of comparing float numbers with the "==" operator, you can use a function like this one.

//compares if the float f1 is equal with f2 and returns 1 if true and 0 if false int compare_float(float f1, float f2) { float precision = 0.00001; if (((f1 - precision) < f2) && ((f1 + precision) > f2)) { return 1; } else { return 0; } } // or bool fequal(float a, float b) { return fabs(a-b) < epsilon; } You can set the precision of the comparison between the floating point numbers by changing the "precision" variable. ==== Usage of the solution ==== To use the solution above for comparing the floating point number 11 and the floating point number x2, you can do : <pre> //we compare our numbers if (compare_float(x1,x2)) { //do something if equal } else { }