Comparison of conditional judgment statements

Comparison of conditional judgment statements

Process Control to make conditional statement judgment, often use a variety of data types of variables and 0 value comparison problem, here is a summary to deepen the understanding of the data type, non-canonical and 0 comparison statements are easy to participate in the comparison of the data types are misunderstood.

§ 1. boolean variable vs. 0 value comparison

bool c99 standard has Boolean type _bool 0 true, 0 for false, if your compiler does not support Boolean types, you can customize the type

Boolean variables cannot be directly compared to TRUE,FALSE , or 1,0 , assuming that the Boolean type is named flag,

The standard if statement that it compares to the 0 value is as follows:

IF (flag)// indicates that flag is true

If (!flag)// indicates flag is False

§ 2. Comparison of integer variables with 0 values

Integer variables should be applied "= =" or "! ="compare directly with 0. Assuming that the integer variable is named value,

It compares the standard if statement with the 0 value as follows:

If (value = = 0)

If (Value! = 0)

§ 3. floating-point variable versus 0-value comparison

There is a precision limit for variables of type float or double , so be sure to avoid using floating-point variables

"= =" or "! ="In comparison with numbers, you should try to convert them into">="or"<="forms. Because float will have an error.

For example, if you assign a float a=0, a may be 0.000000001, there is an error, so use if( x = = 0) to judge, often will not set up. the float_accuracy is the allowable error, the precision, and the standard statement that the floating-point variable a compares to the 0 value is:

Const float float_accuracy = 0.00001;

If ((a >=-float_accuracy) && (a <= float_accuracy))

§ 4. pointer variable versus 0 value comparison

The 0 value of the pointer variable is null (that is, null), although The value of NULL is the same as 0 , but the two have different meanings. Assuming that the pointer variable is named p, the standard statement that compares it to the 0 value is as follows:

If (P = = null)//p is explicitly compared with NULL , emphasizing that p is a pointer variable

If (P! = NULL)

if (null = = P) This is written by the programmer in order to prevent the if (p = = null ) mistakenly writing if (p = null) and intentionally reversed, So this kind of writing is a certain advantage.

Comparison of conditional judgment statements