C language practice (1)

I. A three-day bug

Int fscanf (File * stream, char const * format ,...)

Int scanf (char const * format ,...)

Int sscanf (char const * string, char const * format ,...)

Function to read characters from the input source. The Return Value of the function is the number of input values for conversion.

{

Int A, B;

Sscanf (buffer, "% d", "% d", & A, & B );

}

{

Unsigned int A, B;

Sscanf (buffer, "% d", "% d", & A, & B );

} // An error occurs. The format code is D, which is an integer in decimal format. The data is stored as a signed number. If the integer parameter is longer or shorter than the default integer parameter, omitting a qualifier in the format code is a common error.

{

Unsigned short A, B;

Sscanf (buffer, "% HD", "% HD", & A, & B );

} // Qualifier H. modify the meaning of some format code. HD is no longer the default integer, but short Int.

2. Floating Point comparison

In the program, F1 = F2, but it is clearly equal, but in the program it is done according to the inequality, floating point numbers cannot be compared like this; for example

Float F = 25.095;

If (F = 25.095) printf (,); // The result is that F is not equal to 25.095. This is because the value of 25.095 is expressed as 25.0949999 because it cannot be expressed as a floating point.

We should make a comparison:

If (FABS (F1-F2) <pre-specified precision) // precision 0.00000001 {...}

After a floating point operation, the result is rounded to the memory, which may lead to errors. Therefore, we should try to use high-precision data types, such as when using gcc, we try to use long double instead of double or float, which reduces the chance of many errors. As a general comparison, you can set the difference precision and then compare it.

Complete comparison:

Bool isequal (float a, float B, float abserror, float relerror)
{
If (A = B) Return true;
If (FABS (a-B) <abserror) return true;
If (FABS (A> B) Return (FABS (a-B)/A> relerror )? True: false;
Return (FABS (a-B)/B> relerror )? True: false;
}