The document discusses reference variables in C++. Reference variables allow passing an object to a function without copying it. When declaring a reference variable parameter in a function, an ampersand "&" is used. This creates an alias to the original variable so any changes made to the reference variable are reflected in the original. This avoids copying large objects and allows changing the original variable from within a function.

1. Class No.17 Data Structures http://ecomputernotes.com

6. Reference Variables // example 1 int intMinus1( int oldVal) { oldVal = oldVal – 1; return oldVal; } http://ecomputernotes.com

7. Reference Variables // example 2 int intMinus2( int* oldVal) { *oldVal = *oldVal – 2; return *oldVal; } http://ecomputernotes.com

8. Reference Variables // example 3 int intMinus3( int& oldVal) { oldVal = oldVal – 3; return oldVal; } http://ecomputernotes.com

9. Reference Variables The caller function: calling intMinus1 void caller() { int myInt = 31; int retVal; retVal = intMinus1( myInt ); cout << myInt << retVal; } http://ecomputernotes.com

10. Memory Organization Code Static data Stack Heap Process 1 (browser) Process 3 (word) Process 4 (ourtest.exe) Windows OS Process 2 (dev-c++) http://ecomputernotes.com

12. Reference Variables Call stack layout when intMinus1 is called: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal 31 calling function “caller” called function “intMinus1” stack grows downwards sp

15. Reference Variables Call stack layout after subtraction in intMinus1: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal 31 calling function “caller” called function “intMinus1” stack grows downwards sp 30

16. Reference Variables Call stack layout after return from intMinus1: 1068 31 1072 30 caller’s other stuff myInt retVal calling function “caller” stack grows downwards sp

19. Reference Variables Call stack layout when intMinus2 is called: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal 1072 calling function “caller” called function “intMinus2” stack grows downwards sp

20. Reference Variables Call stack layout after *oldVal = *oldVal – 2; 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal 1072 calling function “caller” called function “intMinus2” stack grows downwards sp 29

21. Reference Variables Call stack layout after return from intMinus2. 1068 31 1072 29 caller’s other stuff myInt retVal calling function “caller” stack grows downwards sp 29

26. Reference Variables Call stack layout when intMinus3 is called: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal calling function “caller” called function “intMinus3” stack grows downwards sp

27. Reference Variables Call stack layout when intMinus3 is called: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal calling function “caller” called function “intMinus3” stack grows downwards sp

28. Reference Variables Call stack layout after oldVal = oldVal - 3: 1052 1060 1068 1056 31 1072 ? caller’s other stuff myInt retVal oldVal calling function “caller” called function “intMinus3” stack grows downwards sp 28

29. Reference Variables Call stack layout after return from intMinus3: 1068 31 1072 28 caller’s other stuff myInt retVal calling function “caller” stack grows downwards sp 28