Chap 5: Functions & Pointers

Question 1

Program execution begins with which function:

Answer 1

main()
is present in every C program. Calls other functions.
drives other function

Question 2

Control flow when calling function calls a function:

Answer 2

The control from calling function is moved to called function and when its execution is completed control is sent back to calling function where it left.

Question 3

All function enjoy a state of equality?

Answer 3

Yes, except for the fact tht execution starts with main. otherwise, nobody is nobody’s boss, all are treated equal. anybody calls anyone. main can be called from somewhere else as well.
Call can be many times.

Question 4

how to call a function? syntax..

Answer 4

functionName();

Question 5

How to define a function?

Answer 5

FunctionName()
{
statement(s);
}

Question 6

Order of defining and order of calling is how?

Answer 6

Not necessarily same. but for readability of program advised to keep it same

Question 7

Recursion:

Answer 7

A program calling itself.

Question 8

Where is defining done?

Answer 8

A program can be called from other function but cannot be defined in other function.

Question 9

Types of function:

Answer 9

User-Defined
Or
Library functions

Question 10

Why use functions?

Answer 10

1. Reduce Retyping of code.

2. Allows separating code in modular functions, which makes it easier to design and understand and test.

Question 11

Passing values between functions:

Syntax

Answer 11

Kernighan and Ritchie method:

fName( x, y, z)
int x,y,z;

OR

ANSI method:
fName( int x, int y, intz )

Question 12

Formal and actual Arguments?

Rules:

Answer 12

Actual arguments are passed when we call the function.
Formal Arg are present with the function where its created.
type, order, number of actual and formal argument should always be the same.
They can have same names but are still treated differently as they are present in different functions.

Arguments aka Parameters

Question 13

Pass a, b, c to calsum() from main:

Answer 13

main()
{
a =4 ; b = 5; c = 6;
sum = calsum( a, b, c);
}

Question 14

Return Statement:

Answer 14

to return a meaningful value back to the calling function.
On executing return the control is immediately sent to the calling function.
return (value);

Question 15

What will happen?

return;

Answer 15

A garbage value is returned.

Question 16

How to prevent function from returning any value?

Answer 16

using void keyword:
void fName()
{  }

Question 17

What will happen?
return(a,b);
return(x,12):

Answer 17

A function can return only one value hence they are both invalid.

Question 18

What if the value of a formal argument is changed?

what happens to actual arguments value in the calling function?

Answer 18

In calling function the value of actual argument does not change.
As a photocopy of values in actual args is made into formal arg. Actual args don’t physically move.

Question 19

Default Scope of a variable?

Answer 19

It’s local to the function in which it is defined.

Question 20

What does calling convention decide?

Answer 20

1. The order in which the arguments are passed to the function.
2. Which function(calling or called) performs clean Up of variables when control returns to called function.

Question 21

When a funct call is encountered and the args are to be passed to a function, what possibilities exist?

Answer 21

1. Args can be passed Left to right
   or
2. R to L

Question 22

The memory of function theory:

Answer 22

The formal args and the local vars defined inside a function are created at a place in memory called stack.
On returning the control, the stack is cleaned up.

Question 23

Output? and explain it.
int a = 1
printf( “%d%d%d”, a, ++a, a++ )

Answer 23

331
not 122, as C’s calling convention, is R to L.
So 1 goes through a++ (1 passed and then incremented to 2) first
then ++a ( 2 incremented to 3 , 3 passed)
and then a (a is now 3, 3 passed).
printf() collects the values in the order in which we have asked it to get them printed (not in the order in which they were passed).

Question 24

Standard calling convention:

Answer 24

Args are passed to function right to left.

Stack is cleaned up by the called function.

Question 25

math.h

Whats .h for? and other theory regarding it..

Answer 25

Whenever we call the library functions we must write their prototype before making a call, helps compiler to check whether the values being passed and returned are as per the prototype declaration.
But we don’t define them, just call them so we may not necessarily know the prototype. Hence library of functions is provided a set of ‘ .h ‘ files.

These contain prototypes.
Lib functions are divided in different groups and one file is provided for each group. Ex: math functions has ‘ math.h’

Question 26

Default return value:

As when prototypes were not used.

Answer 26

int

Question 27

Prototype Declaration:

Answer 27

Example:
float Fname( float );

 It says Fname receives float and returns float.
in main() its done in the body, but if other functions are calling Fname then just make one declaration at the top, outside all those functions.

Question 28

How to make a function return a value other than int?

Answer 28

To do so, it is necessary to explicitly mention so in calling function and called function.
While declaring:
float Fname( float x)
{                    
   return (y);
}
and prototype declaration in calling func.

Question 29

Calls by value?

Answer 29

Passing values of variables to the called function.

Question 30

What is an address?

Answer 30

location number of variable.

Question 31

Calls by reference:

Answer 31

Passing the location number of variable(address) to a function.

Question 32

%u

Answer 32

Format specifier for an unsigned integer.

Like address of variables is not associated with any sign so %u could be used for address.

Question 33

What is operator * ?

Syntax to use?

Answer 33

• Value at address
• Indirection Operator.
  *(address), *(&i)
  i = *(&i)

Question 34

int i = 3;

What 3 things does this tell to compiler?

Answer 34

1. Reserve space in memory to hold int value.
2. Name that location i.
3. Store value 3 in that location.

Question 35

What is a pointer?

Answer 35

A pointer is a variable that contains address, and addresses are always a whole number so, pointers always contain whole number.

Question 36

what do u understand by
int *j;
char *ch;

Answer 36

well j and ch are pointers who will contain address (whole numbers).
Value at address contained in j is integer.
Value at address contained by ch is a char.

Question 37

Whats a pointer containing pointer?

Answer 37

that will be k
int i,*j,k;
*j = i; k = &j;
so, i = *j, &i = *k, i = **k

Question 38

Consequences of call by reference:

2

Answer 38

1. since we are sending the address to the function, the function will now be manipulating the actual arguments.
   also in functions, now use pointers to do operations, (value at address is to be manipulated not address)
2. Allows us to return more than one value.

Question 39

Recursion: how’s it possible?

Answer 39

aka Circular definition, recursion is a process of defining something in terms of itself.
Successive INVOCATIONS of the same function are possible because the compiler keeps track of which invocation calls which.

Question 40

Data Structure:

Answer 40

Ways of organising the data.

Question 41

LIFO:

Answer 41

Last in First Out data structure is the one where the last item to get stored on the stack( Push operation ) is the first one to get out of it (Pop Operation).

Question 42

What do you mean by stack?

[not the working]

Answer 42

The stack is a data structure for implementing normal, recursive function.
It’s a Last In First Out (LIFO) data structure.

Question 43

Cdecl Calling Convetion:

Answer 43

called function clears the retunring value and return address, when control passed to calling function at return address it cleans the parameters and therefore entire stack.

Question 44

How is normal function implemented using Stack:

Answer 44

When calling F calls f, the values of parameters are pushed in the stack ( remember C using std calling convention, Right to left) followed by the return address ( address of statement right after).
Then the control is sent to f, during execution local variables get pushed on the stack. On encountering return, return value is popped and then the return address and the control goes back to F, before execution of next statement stack is cleared.

Question 45

How are values being pushed and popped even though we didn’t write any code for it?

Answer 45

The compiler on encountering a function call generates a code to push parameters and the address. lly it generates code to clear the stack when control returns from f to F.

Question 46

Blunder resulting stack is full:

Answer 46

Not using the base case in recursive Func.
It must include an if statement to force return won’t recursive call being executed otherwise it would keep pushing parameters n return address and u would fall in indefinite loop and stack would get full.

Question 47

Implementation of recursive function:

Answer 47

Whenever a recursive call is made the parameters and return address gets pushed on the stack. The stack gets unwound when called function returns control back.
- Thus during every recursive function call we are working with a fresh set of parameters.

Question 48

Benefit of adding function to the lib?

Answer 48

F added to the lib are first compiled and then added. so saves compilation time.

Question 49

Creating a new lib:

Answer 49

Its possible, make sure u make header file (.h) which contains the prototypes.