Functions, type conversions and visibility

Question 1

What are function prototypes?

Answer 1

A function should be declared ( need not be defined ) before it is used.

(If not declared, then C is will assume the prototype)

Function prototypes are used for this. They are a line of code that can be used to declare a function without the need of the body of the function.

Question 2

What is a header file?

Answer 2

A header file is a file that is designed to be used in multiple files and contains function prototypes as well as struct definitions.

Question 3

What is the use of type def?

Answer 3

Type def is used to give new names to types

eg: typedef unsigned int day, month

day or month can be used for the unsigned int type

Question 4

what is casting or type casting?

Answer 4

Type casting converts values from one type to another type implicitly or explicitly

Storing a float into an int is implicit casting

you can also explicitly type casting to an int by using (int)

Question 5

What should you need to watch out for when casting?

Answer 5

There is no error checking in casting

unsigned int i = -1

since unsigned int cannot store negative values, in this case, i will be 2^32 - 1

unsigned char c = 300,

Question 6

What is declaration and definition in the case of a function and variables?

Answer 6

Variables:

• Declaration is specifying the type of the variable without defining it
• Variables can be declared several times but it can only be defined once

Functions:

• Declaration is the prototype
• Prototypes can be specified in different files but the function can be defined in only place

Question 7

What are the different ways to define a variable so that they work in multiple files?

Answer 7

There are 2 ways to define a variable in multiple files

• Static: The variable is unique to this file
• extern: The variable is defined in some other file, but it is going to be used in this file that defines it.

Question 8

What happens when a static variable is defined and used in a function

Answer 8

When a static variable is defined inside a function then it is effectively global as in the same value persists when the function is called again.

inf get_number(){

static int i = 0;

i++;

}

Question 9

what does the following do?

1. clang -c prog.c
2. clang prog.o -o prog
3. clang -c prog.c lib.c
4. clang prog.o lib.o -o myfile

Answer 9

1. creates an object file prog.o
2. links the object file prog.o into an executable file prog
3. compiles source into prog.o and lib.o
4. links prog.o and lib.o into executable myfile

Question 10

What are make files?

Answer 10

Make files contains rules that are used to make a program.

A make file only recompiles any new changes

Question 11

What to watch out for when using make?

Answer 11

Use of tabs instead of spaces and also the default target for make is the first target.

Question 12

Which 2 data types can switch statements take in?

Can the switch cases be variables?

Answer 12

Integers and enums

Switch statements should be constant

Question 13

What to watch out for when using arrays in C?

Answer 13

• Arrays are not bounds checked
• No way to get the length of the array
• You cannot return an array from functions
• Cannot assign one array to another array
• Equality check would only check to see if the arrays are the same object.

Question 14

What happens when you assign an a value to an array that is not within the bounds?

Answer 14

When an array is assigned out of bounds then it leads to a undefined behaviour.

Question 15

What is the null character and what is it used for?

Answer 15

The null character ‘\0’ is just the 0 of the char type, it denotes the end of a string that is represented by a character array.

Question 16

What is the first command line argument arg[0] given to a program

Answer 16

The first argument given to a program, is the program name.

arg[0] is the name of the program.

Question 17

What is #define

Answer 17

It is a preprocessor directive and it is used to give aliases. The aliases are replaced by the actual code before the compilation of the code.

Question 18

What are macro functions?

Answer 18

define double(X) X*X

Macro functions use simple text based substitution

Question 19

What are some of the uses of macro functions?

Answer 19

• Don’t need to worry about types
• Useful for things that aren’t valid code, like using anything apart from ints and enums in switch statements.

Question 20

What are header guards?

Answer 20

Header guards are macro guards that helps avoid double inclusion when working with the #include preprocessor directive