va_list is
Answer: B
Correct answer: a predefined data type in stdarg.h
va_list is a type - a typedef declared in <stdarg.h> - used to declare the object that holds the state of the walk through the variable arguments. va_start, va_arg and va_end are the macros that operate on it.
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What is the output of this program?
#include <stdio.h>
#define p 17;
int main()
{
printf("%d",p);
return 0;
}
Answer: D
Correct answer: Compilation error
The macro body is 17; - semicolon included. Substituting it gives
printf("%d",17;);
which is a syntax error. This is why a #define for a constant should never end with a semicolon: the macro is text, and the semicolon travels with it wherever the name is used.
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# include <stdio.h>
# define scanf "%s Geeks Quiz "
int main()
{
printf(scanf, scanf);
return 0;
}
Answer: D
Correct answer: %s Geeks Quiz Geeks Quiz
scanf is redefined as a string literal, so the call expands to
printf("%s Geeks Quiz ", "%s Geeks Quiz ");
The first copy is the format string and the second is the argument that its %s consumes. The %s is replaced by the whole second string, so the output is %s Geeks Quiz Geeks Quiz. Nothing stops a macro from shadowing a standard library name, which is exactly why it is a bad idea.
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The NULL character indicates an end of a string and a file.
Answer: B
Correct answer: FALSE
The null character marks the end of a string in memory, and nothing more. A file’s end is not marked by any byte within it: it is known from the file’s recorded length, and reported to the program as EOF. A file may perfectly well contain null bytes as data - every binary file does.
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Once preprocessing is over and the program is sent for the compilation the macros are removed from the expanded source code.
Answer: A
Correct answer: True
Preprocessing produces a translation unit in which every macro has been expanded and removed - no #define, and no macro name, survives into what the compiler parses. That is why a macro has no type, occupies no storage, and cannot be inspected in a debugger.
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What will be the output of the following C code?
#include <stdio.h>
void main()
{
#ifndef max
printf("hello");
#endif
printf("hi");
}
Answer: B
The code shown above illustrates the preprocessor directive #ifndef. If the identifier checked is not defined, then the statements following #ifndef are executed. Here, since the identifier max is not defined, the statement after #ifndef is executed. Hence the output is: hellohi
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Macros with arguments are allowed
Answer: A
Correct answer: True
Function-like macros with parameters are ordinary: #define MAX(a,b) ((a) > (b) ? (a) : (b)). The arguments are substituted as text, which is why the parameters and the whole body need parenthesising and why an argument with a side effect can be evaluated more than once.
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Which of the following are correctly formed #define statements in C?
Answer: C
Correct answer: #define CUBE(X)(X*X*X)
The others each have a fault:
#define CUBE (X) (X*X*X); - the space after the name makes it an object-like macro whose body is the whole rest of the line, and the trailing semicolon travels with every use.#define CUBE(x) (X*X*X) - the parameter is x but the body uses X, so the argument is never substituted.#define CUBE(X) {X*X*X} - braces make it a block, which cannot appear where a value is wanted.Only the third is well formed - though ((X)*(X)*(X)) would be safer still.
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What will be the output of the following C code?
#include <stdio.h>
#define san 557
main()
{
#ifndef san
printf("yes");
#endif
printf("no");
}
Answer: C
Correct answer: no
san is defined, so #ifndef san is false and the printf("yes") between it and #endif is deleted before compilation. Only the unconditional printf("no") remains, so the output is no.
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The translator which performs macro calls expansion is called:
Answer: C
Correct answer: Macro pre - processor
Macro expansion is done by the macro preprocessor, the phase that runs before compilation proper: it handles #include, #define and the conditional directives, and hands the compiler a file with no directives left in it. The linker, by contrast, works after compilation on object files.
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