Answers

---

1. The #include <stdio.h> is missing and the variable p has not been declared.

2. The equals sign can only be used in a declaration to initialise a variable. Therefore it should be

   
   int	x=95, y =95;
   

3. x = x - 1;
   x --;
   --x;
   x -= 1;
   

4. • missing ;
   • not valid - should be k = 64/4;
   • not valid
   • valid x = 6
   • valid
   • not valid
   • valid x = 5

---

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Back to Main Page for Lecture 2

 


  

 

 Control Constructs 
 

 





 What is wrong with the following?

int x;
if (x=1)
	x++;



What is wrong with the following?

int x, y, z;

if (x > y && < z)
	x = y;



Write an extract of code to test if the variable x is a positive
number?


Write an extract to test if the variable x is a positive and even
number?







 Answers
                                        











































































 The test should be  x== 1, with x=1 this will assign
the value of 1 to x rather than checking if x is a 1.


Assuming that it is intended to compare z to z, the test should be  x >
y && x < z 


 if (x > 0)



 if (x > 0 && x%2 == 0)






 


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Back to Main Page for Lecture 3 



                                        








 


  

 

 Iteration 
 

 






Change to following code to a while loop.

int	x, y;
for (x=1; x < 57; x+= 2)
	y = x;



What is wrong with the following?

int	n=0;
while (n < 100)
	value = n*n;


 Write a while loop that calculates the sum of all numbers
between 0 and 20 inclusive?


Convert the above loop to a  do ... while  loop.


Convert the above loop to a for loop.


What is wrong with the following?

i = 1;
while (i <= 10 )	
	printf("%d\n", i);
	i++;

	





 Answers
                                        










































x = 1;
while (x < 57)
{
	y = x;
	x += 2;
}


The value of n within the loop is never incremented. It will therefore always
have a value of 0, which is less than 100, and hence this will produce an
infinite loop which will never terminate. The program will therefore
never end.


int	i, sum =0;
i = 0;
while (i <= 100)
{
	sum += i;
	i++;
}


int	i, sum =0;
i = 0;
do
{
	sum += i;
	i++;
}while (i <= 100);


int	i, sum =0;
for (i=0; i <= 100, i++)
{
	sum += i;
}


There are no braces around the printf() and increment i statements, therefore
it will execute only the printf() statement within the loop, and an infinite
loop will again occur.




 


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Back to Main Page for Lecture 4 



                                        








 


  

 

 Functions 
 

 





 Explain the difference between a function declaration and a functions
definition? Where is the function declaration placed?


Given the following function declarations, explain the meaning of each.


int function1(int a, float b);
   void function2(float a, float b, float c);
int function3(void);
float function4(float x);
void function5(void);



Write an appropriate function call for each of the function declarations given above.


What does the following function do?
float function(float a, float b, float c)
{
	float tmp;

	tmp = (a + b + c )/ 3.0 ;

	return tmp;
}



Give an example function call for the above function.



Give the function declaration for the function given in question 4.







 Answers
                                        
















































 The declaration is contained within the program before the function is called. It
is usually
outside any function, including the main program. It contains details of the function
name, the return type and the types of the function arguments.

The definition contains the actual code of what is to be implemented when the function
is called.

 

 The function is sent an integer argument which it will refer to as a
within the function and a floating point variable, which it will refer to as
b within the function. The function will return an integer quantity.

The function is sent 3 floating point arguments and returns no value to the calling
program.

The function is sent no arguments but returns an integer. 

The function is sent one floating point argument and returns a floating point
argument.
 The function is sent no variable and returns nothing.


 Example calls are given below, 

 
int x, z;
float y;

/* x and y are assigned some values in the program */

z = function1(x, y);



float	x,y,z;

/* x, y and z assigned values in program */

function2(x, y, z);


int a;

a = function3();


float a, b;

/* b assigned a value in program */
a = function4(b);


 
function5();




It returns the average value of the three values sent to it.


x = function(a,b,c);


 float function(float, float, float); or float function(float a, float
b, float c); 






 


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