What are the various conditional syntax of preprocessor in C?
The preprocessor conditional compilation directive spans several lines: The condition specification line (beginning with #if , #ifdef , or #ifndef ) Lines containing code that the preprocessor passes on to the compiler if the condition evaluates to a nonzero value (optional) The #elif line (optional)
What is #if and #endif in C?
The #if directive, with the #elif, #else, and #endif directives, controls compilation of portions of a source file. If the expression you write (after the #if) has a nonzero value, the line group immediately following the #if directive is kept in the translation unit.
What is conditional directive in C?
The conditional directives are: #ifdef – If this macro is defined. #ifndef – If this macro is not defined. #if – Test if a compile time condition is true. #else – The alternative for #if.
What is if define with example?
An if statement is a programming conditional statement that, if proved true, performs a function or displays information. Below is a general example of an if statement, not specific to any particular programming language. if (X < 10) { print “Hello John”; }
What is conditional preprocessor?
A conditional is a directive that instructs the preprocessor to select whether or not to include a chunk of code in the final token stream passed to the compiler.
What is the difference between #if and if?
#if is a preprocessor directive. This is evaluated in the first stage of compilation and by the time that your C++ code is ready to be executed at run time, those #if’s (or any directives) are no longer there. #if and if both evaluates some expression that can be deduced to a boolean value.
What is the syntax of if?
The syntax for if statement is as follows: if (condition) instruction; The condition evaluates to either true or false. True is always a non-zero value, and false is a value that contains zero.
What does #ifndef mean in C?
In the C Programming Language, the #ifndef directive allows for conditional compilation. The preprocessor determines if the provided macro does not exist before including the subsequent code in the compilation process.
What does endif mean in C?
In the C Programming Language, the #endif directive is used to define the following directives: #if, #ifdef , and #ifndef . Whenever the #endif directive is encountered in a program, it determines if the preprocessing of #if, #ifdef, or #ifndef has been completed successfully.
What is difference between if if and if else if?
In if, the statements inside the if block will execute if the condition is true and the control is passed to the next statement after the if block. In the if else, if the condition is true, the statements inside the if block execute and if the condition is false the statements in the else block execute.
What is if statement in C syntax?
C if Statement The if statement evaluates the test expression inside the parenthesis () . If the test expression is evaluated to true, statements inside the body of if are executed. If the test expression is evaluated to false, statements inside the body of if are not executed.
What is Ifndef and endif?
#ifndef /* code */ #else /* code to include if the token is defined */ #endif. #ifndef checks whether the given token has been #defined earlier in the file or in an included file; if not, it includes the code between it and the closing #else or, if no #else is present, #endif statement.
What is the difference between Ifdef and Ifndef?
Use the #ifdef statement when you want to compile a section only if a specified expression has been defined with #define. Use #ifndef when you want to compile a section only if a specified expression has not been defined.
What is a preprocessor in C programming?
C – Preprocessors. The C Preprocessor is not a part of the compiler, but is a separate step in the compilation process. In simple terms, a C Preprocessor is just a text substitution tool and it instructs the compiler to do required pre-processing before the actual compilation.
What is the difference between preprocessor expressions and preprocessor symbols?
In your example c is a compiler generated symbol, c has no value until run-time, whereas preprocessor expressions are evaluated at build-time (in fact as the name suggests before the compiler processes the code), so can only operate on pre-processor symbols which do exist at build time.
How does the preprocessor know how to parse C variables?
The preprocessor is run on the text, before any compilation is done. It doesn’t know how to parse C. What you probably wanted instead of int c=1; was The key here is that this is all defined before compile time. The preprocessor doesn’t care about C variables, and certainly doesn’t care what their values are.
What is a condition in C preprocessor?
A conditional in the C preprocessor resembles in some ways an if statement in C, but it is important to understand the difference between them. The condition in an if statement is tested during the execution of your program. Its purpose is to allow your program to behave differently from run to run, depending on the data it is operating on.