C - Hello, World

Question 1

What are the 3 general steps in creating an executable?

Answer 1

1. Preprocessing
2. Compiling
3. Linking

Question 2

What is preprocessing?

Answer 2

Before code is compiled it is given to a program called the preprocessor. The preprocessor edits and manipulates code, setting it up for the compiler. Typically the preprocessor looks for lines that begin with # and alters the code based on these directives.

Question 3

What is compiling?

Answer 3

Preprocessed code is given to the compiler, a program that translates C statements into machine instructions.

Question 4

What is linking?

Answer 4

A linker combines the object code produced by the compiler with any additional code needed to create a complete execuatable. This additional code includes things like library functions.

Question 5

What are the three fundamental language features that C relies on?

Answer 5

1. Directives
2. Fuctions
3. Statements

Question 6

What is a function?

Answer 6

A series of statements grouped together and given a name

Question 7

What does main return?

Answer 7

An integer status code

Question 8

How do you start all c programs?

Answer 8

include

int main(void)

Question 9

Why include a header file in a C program?

Answer 9

to use standard libraries

Question 10

What are the steps for building C programs?

Answer 10

preprocessing, compiling, linking. (Using gcc usually executes all three steps automatically.)
in console:
>gcc -o hello hello.c
>./hello

Question 11

What is pre-processing?

Answer 11

Pre-processing: processing directives,
modifying source file text

Question 12

What is compiling?

Answer 12

Compiling: translating source code into
machine instructions (object code)

Question 13

What is linking?

Answer 13

Linking: combining object code created
by compiler with other code to create a
single executable program

Question 14

What are comments?

Answer 14

They are text for documentation purposes and are mapped to whitespaces before preprocessing. (Neither pre-processor nor compiler sees them.)

Question 15

What is a variable

Answer 15

it has a name, a type and a value. It can be assigned values, do calculations and in-/output variable

Question 16

What are control structures in C?

Answer 16

Two types:
 Selection
* if statement
* switch statement
 Loops
* while loop
* do while loop
* for loop

Question 17

What does the Pre-processor do?

Answer 17

Removes comments
Modifies source code
according to preprocessor directives
Most importantly:
includes header files into
source code

Question 18

What are the steps to compiling a program in C?

Answer 18

Step 1: Pre-Processor. Removes comments, reads pre-directives, includes header files. Output: Translation Unit,
Step 2: Compiler. Performs correctness checks, code optimizations. Output: assembler code (.s file),
Step 3: Assembler. Translates assembler code (.s file) into binary machine instructions/object code (.o file),
Step 4: Linker. Combines multiple object files into a single file, Output: exe file.

Question 19

What is the use of a header guard in preprocessing?

Answer 19

Use: to avoid including a header file more than once, check if it has already been included.
Ex:
grandparent.c
#ifndef GRANDPARENT_H
#define GRANDPARENT_H
struct foo{
int member;
};
#endif
….
in parent.c
#ifndef PARENT_H
#define PARENT_H
#include “grandparent.h”
#endif

Question 20

What is the difference between variable definition and declaration?

Answer 20

Variable declarations can be duplicated, have static name type binding done at compile time and specifiy identifier and type.

Variable definition: only one allowed, assigns fixed address to variable (at runtime?).

Definition and declaration of VARIABLE looks the same, possible: int a; but not so for functions.

Question 21

What is initialization of a variable?

Answer 21

Initialization: assigns initial value to a variable, value not needed at compile time. Assigns scope-

Question 22

What is scope?

Answer 22

Scope is the portion of program where name of variable (identifier) can be used to refer to a variable.

Question 23

How to compile a file world.c in both gcc and clang?

Answer 23

gcc world.c -std =c90

clang world,c -std=c99

Question 24

what are the different compiler options and what are their uses?

Answer 24

The different compiler options are

-o: Name your executable
-g: Add in debugging information
-Wall: Give warnings
-Wextra: Give additional warnings
-O, O2, O3: Compiler optimization and different levels of it.

Question 25

What are relational operators?

Answer 25

A binary operator that tests a relationship between two entities and produces true or false:

, <=, >=

Question 26

What is an equality operator?

Answer 26

A binary operator that tests equality or lack of equality between two entities:

!=

Question 27

Variables always have a type.

Answer 27

Syntax:
type var_name;

Example:
char c;
int n;

Question 28

Logical operators
|| OR, && AND, ! NOT

Answer 28

expression1 || expression2 - if one of the 2 expressions is true, then the whole expression is true

expression1 && expression2 - if one of the 2 expressions is false, then the whole expression is false

!expression - if the expression is false, then the whole expression is true. If the
expression is true, then the whole expression is false.

The value of the whole expression is 0 if false, something else if true

Question 29

Comparisons

Answer 29

< Less than
<= Less or equal to
== Equal to
>= Greater or equal
to
> Greater than
!= Different than

Question 30

expression operator expressionExamples:
(a + 32) < 98
b == a
c >= f () + 402

Answer 30

The value of a comparison is 0 if false, and
something else if true.