Lab Sheet 2
Additional Features in C++
Manipulators
Manipulators are operators that are used to format the data display. The most commonly used manipulators are endl and setw. The endl manipulator, when used in an output statement, causes a linefeed to be inserted. It has the same effect as using the newline character "\n" in C. For example
...
cout<< "LODGING" <<lexp<<endl;
cout<< "CLOTHING" <<cexp<<endl;
cout<< "TRAVELING" <<texp<<endl;
.....
If we assume that values of variable lexp, cexp and texp are 2000, 800, and 2500 respectively, then output appears as
LODGING 2000
CLOTHING 800
TRAVELING 2500
It is not the ideal output. setw(n) manipulator eliminates this problem by specifying filed width. The value is right-justified within the field. For example
...
cout<<setw(11)<< "LODGING" <<setw(8)<<lexp<<endl;
cout<<setw(11)<< "CLOTHING" <<setw(8)<<cexp<<endl;
cout<<setw(11)<< "TRAVELING" <<setw(8)<<texp<<endl;
.....
the output of this section is
LODGING 2000
CLOTHING 800
TRAVELING 2500
Namespace
The namespace feature in C++ allows us to specify a scope with a name, that is, the namespace is a named scope. The namespace feature helps us to reduce the problem of polluting the namespace. A namespace is defined as follows.
namespace nsn
{
int item;
void showitem(int it)
{
cout<<it;
}
}
The elements from the namespace are used as
cout<<nsn::item;
or it can be accessed by including the particular element into our scope as
using nsn::item;
after inclusion the statements
cout<<item; //correct
showitem(item); //not correct
We can also include everything from the namespace as
using namespace nsn;
After this inclusion, every element from the namespace can be used directly as
cout<<item;
showitem(item);
Pass by reference
When an address of the variable/object is passed, the function works directly on the actual variable/object used in the call. This means that any changes made to the variable/object inside the function will reflect in the actual variable/object. The function prototype of the function that allows pass by reference is:
return_type function_name(datatype &pram_name, datatype &pram_name);
For example
void swap (int &x, int &y)
{
int t;
t=x;
x=y;
y=t;
}
This function can be called as
swap(a,b); //reference of a and b is passed
Return by reference
The primary reason for returning the value by reference is to use a function call on the left side of the equal sign. In this case, the function should return a reference to variables, but not the values.
For example
int x=5;
int & asgnx()
{
return x;
}
This function can be called as
asgnx()=7; //x is assigned with value 7
Structure with function
The value of the structure variable can be passed as a parameter to a function. For example
struct student
{
...
};
...
void show(student st ); //prototype
...
show (st1); //function call, st1 is student structure variable.
Overloaded function
The overloaded function appears to perform different operations depending on the kind of data sent to it. It performs one operation on one kind of data but another operation on a different kind. The reason behind using the overloaded function is because of its convenience to use the same function name for different operations.
void convert(); //takes no argument
void convert(int n); //takes one argument of type int
void convert(float,int); //takes two argument of type float and int
It uses the number of arguments, and their data types, to distinguish one function from another. The function definition and call can be done as usual.
Inline Function
We know that function saves memory space but takes some extra time. If the functions are short, they may be put directly in the call location of the calling function. If the function is very short, the instructions necessary to call it may take up as much space as the instructions within the function body, so that there is not only a time penalty but a space penalty as well. The solution to this is the inline function. This kind of function is written like a normal function in the source file but complies to inline code instead of a function. Besides, the source file remains well organized and easy to read, since the functions are shown as a separate entity. Functions that are very short, say one or two statements are candidates to be inlined.
inline(keyword) float(retutn type) convert(int n)
i.e
inline float convert(int n)
Here all we need is the keyword inline in the function definition.
Default Arguments
A function can be called without specifying all its arguments. This won't work on just any function. To make a function accept missing arguments has to specify the default value of those missing arguments.
Let us see an example
void dearg(char ch = '?', int n = 25); //declaration with default arguments
int main()
{
dearg();
dearg('<');
dearg('>',30);
return 0;
}
void dearg(char ch, int n)
{
...
}
Here the function dearg() takes two arguments. It is called three times from the main() function. The first time it is called with no arguments, second time with one argument and third time with two. The first and second provides default arguments, which will be used if the calling function doesn't supply them. The values for default arguments follow an equal sign, which is placed directly after name. It is also possible to use variable name. If one argument is missing it assumed to the last argument as we show in second.
Exercises
Use manipulators where seems to be useful.
Write a program to set a structure to hold a date (mm,dd and yy), assign values to the members of the structure and print out the values in the format 11/28/2004 by function. Pass the structure to the function
Write a program using the function overloading that converts feet to inches. Use function with no argument, one argument and two arguments. Decide yourself the types of arguments. Use pass by reference in any one of the function above.
Define two namespaces: Square and Cube. In both the namespaces, define an integer variable named "num" and a function named "fun". The "fun" function in "Square" namespace, should return the square of an integer passed as an argument while the "fun" function in "Cube" namespace, should return the cube of an integer passed as an argument. In the main function, set the integer variables "num" of both the namespaces with different values. Then, compute and print the cube of the integer variable "num" of the "Square" namespace using the "fun" function of the "Cube" namespace and the square of the integer variable "num" of the "Cube" namespace using the "fun" function of the "Square" namespace.
Write a function that passes two temperatures by reference and sets the larger of the two numbers to a value entered by user by using return by reference.
Assume that employee will have to pay 10 percent income tax to the government. Ask user to enter the employee salary. Use inline function to display the net payment to the employee by the company.
Write a program that displays the current monthly salary of chief executive officer, information officer, and system analyst, programmer that has been increased by 9, 10, 12, and 12 percentages respectively in year 2010. Let us assume that the salaries in year 2009 are
Chief executive officer Rs. 35000/m
Information officer Rs. 25000/m
System analyst Rs. 24000/m
Programmer Rs. 18000/m
Make a function that takes two arguments; one salary and the other increment. Use proper default argument.