Parameter Passing

Question

Predict the Output for both the snippets for the following:
1. Call by Value
2. Call by Reference
3. Call by Need
4. Call by Name
5. Call by value Result/Call by value Return(Copy Restore)
6. Call by Text

Answer 1

1- Call by value

int a = 100; // Global variable
void P(int x) 
{ 
    a = 1000; // this will update global variable a 100 to 1000.
    print(x); // will print value of x which is local to function P 100.
    a = a + 20; // expression will be executed as 1000 + 20 and will be stored in a as 1020.
    x = x + 10; //expression will be executed and it will update the local variable x as 100 + 10 = 110.
    print(x);  // will print the local value of x which is 110.
}
void main()
{
    P(a); // This will pass global a which is 100.
}

//after completion of program a will have the final value as 1020.

 

2- Call by reference

int a = 100; // Global variable
void P(int *x) 
{ 
    a = 1000; // this will update global variable a 100 to 1000.
    print(*x); // will print value of a which is pointed by integer pointer x, 1000.
    a = a + 20; // expression will be executed as 1000 + 20 and will be stored in a as 1020.
    *x = *x + 10; //expression will be executed and it will update global variable a which is pointed by x as 1020 + 10 = 1030 and 1030 will be updated in global variable a.
    print(*x);  // will print the value pointed by x which is global variable a 1030.
}
void main()
{
    P(&a); // This will pass  address of global variable a.
}

//after completion of program a will have the final value as 1030.

 

3- Call by name

int a = 100; // Global variable
void P(int x) // every x will be replaced by a.
{ 
    a = 1000; // this will update global variable a 100 to 1000. 
    print(x) print(a); // will print value of global a which is 1000. 
    a = a + 20; // expression will be executed as 1000 + 20 and will be stored in global a as 1020. 
    x = x + 10 a = a + 10; //expression will be executed and it will update the global variable a as 1020 + 10 = 1030. 
    print(x) print(a); // will print the global variable a which is 1030.
}
void main()
{
    P(a); // This will pass value of global a which is 100.
}

//after completion of program a will have the final value as 1030.

 

4- Call by value result

int a = 100; // Global variable
void P(int x) 
{ 
    a = 1000; // this will update global variable a 100 to 1000.
    print(x); // will print value of x which is local to function P 100.
    a = a + 20; // expression will be executed as 1000 + 20 and will be stored in a as 1020.
    x = x + 10; //expression will be executed and it will update the local variable x as 100 + 10 = 110.
    print(x);  // will print the local value of x which is 110.
} //once the method calling will over all formal parameter will be dumped into actual parameter, value of x will be dumped into global a so a value will be replaced from 1020 to 110.

void main()
{
    P(a); // This will pass global a which is 100.
}

//after completion of program a will have the final value as 110.

 

5- Call by need (this is not good example for call by need so I am modifying some lines to understand concept better)

int a = 100; // Global variable
void P(int x) // temp value will be passed in x.
{ 
    a = 1000; // this will update global variable a 100 to 1000.
    print(x); // will print value of x and in x temp value is stored, 110.
    a = a + 20; // expression will be executed as 1000 + 20 and will be stored in a as 1020.
    print(x + 10);  // expression will be executed as 110(temp value) + 10 = 120 and will print 120.
}
void main()
{
    P(a + 10); // execute the expression as 100 + 10 = 110 and will store in temp variable.
}

//after completion of program a will have the final value as 1020.