Call by Value
In the Call by Value method, the called function creates new
variables to store the value of the arguments passed to it.
The following program illustrates the invoking of a function
//This function swaps the value of two variable
void swap(int, int);
int iVar1, iVar2;
cout<<"Input two numbers "<<endl;
cout<<"In main "<<iVar1<<" "<<iVar2<<endl;
void swap(int iNum1, int iNum2)
iTemp = iNum1;
iNum1 = iNum2;
iNum2 = iTemp;
cout<<"In swap "<<iNum1<<" "<<iNum2<<endl;
The sample output of Program 7.4 is:
Input two numbers
In swap 25 15
In main 15 25
In Program 7.4, values entered for the variables iVar1 and
iVar2 are passed to the function swap(). When the function
swap() is invoked, these values get copied into the memory
locations of the parameters iNum1 and iNum2, respectively.
This is depicted in the following figures(refer Figure 7.1
Therefore, the variables in the calling function main() are
distinct from the variables in the called function swap() as
they occupy distinct memory locations.
In Program 7.4, the function arguments are passed by value.
When arguments are passed by value, the called function
creates new variables of the same data type as the arguments
passed to it. The values of these arguments are copied into
the newly created variables. Passing arguments by value is
useful when the function does not need to modify the values
of the original variables in the calling program. Therefore,
the values of the variables in the calling functions do not
get affected when the arguments are passed as values.
A reference variable provides an alias- an alternate name-
for the variable. A reference variable is declared by
preceding the variable name with an ampersand (&). The
following statements declare a reference variable called
int &refer = num;
In the statements given above, refer is a reference variable
or alias to the variable num. A reference declaration allows
a variable name and the reference name to be used
interchangeably. Both the variable and its reference share
the same memory address.
The following program illustrates the use of reference
//This program illustrates the use of reference variables
int number = 5;
int &ref = number;
cout<<"Number is "<<number<<endl;
cout<<"Incresing the number......"<<endl;
cout<"Number now is "<<number<<endl;
cout<<"Reference now is "<<ref<<endl;
cout<<"Number now is "<<number<<endl;
In Program 7.5, the statement
increments the value of the variable number by 1, the value
of the variable number therefore becomes 6. The statement:
again increments the value of the variable number by 1
because ref points to the same memory location as number.
The output of program 7.5 is:
Number is 5
Increasing the number........
NUmber now is 6
Reference now is 7
Number now is 7
A reference variable can be initialized only when it is