Functions Pass by Value Pass by Reference

1
Functions-----------Pass by ValuePass by
Reference

• SI 204

2
Arguments vs. Parameters

• Arguments
• function call
• actual values passed to function
• Parameters
• Placeholder in function heading waiting for
  arguments

answer cube (x) double cube (double inputVal)
Argument (function call)
parameter (function heading)
3
What is the output?

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

Call by Value
??
5
4
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
X
?
results
DoubleIt
5
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
DoubleIt
6
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
?
DoubleIt
?
y
7
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
X
results
?
?
DoubleIt
?
y
8
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
?
DoubleIt
5
9
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
?
DoubleIt
5
10
10
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
10
DoubleIt
10
11
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
?
10
DoubleIt
10
12
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
X
results
10
10
DoubleIt
13
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
X
results
10
?
DoubleIt
14
Call by value Sending a copy

• int DoubleIt (int)
• int main ( )
• int x 5
• int results DoubleIt (x)
• cout ltlt x
• return 1
• int DoubleIt (int y)
• y 2y
• return y

5
X
results
10
?
DoubleIt
15
What is the output?

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y) // Function Definition
• int z y
• y 2 y
• return y z

Call by Reference
??
14,21
16
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y) // Function Definition
• int z y
• y 2 y
• return y z

TripleIt
7
x
17
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y) // Function Definition
• int z y
• y 2 y
• return y z

?
results
TripleIt
7
x
18
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
TripleIt
7
x
19
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
?
TripleIt
7
x
20
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

results
?
?
TripleIt
7
y, x
21
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
?
TripleIt
7
7
z
22
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
?
TripleIt
7
14
7
z
23
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
21
?
TripleIt
14
7
z
24
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

?
21
TripleIt
14
7
z
25
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

results
21
21
TripleIt
14
x
26
Call by reference Getting the original

• int TripleIt (int) // Prototype
• int main ( ) // Function Definition
• int x 7
• int results TripleIt (x)
• cout ltlt x ltlt , ltlt results
• return 1
• int TripleIt (int y)
• int z y
• y 2 y
• return y z

results
21
?
TripleIt
14
x