Passing Parameters

Different Techniques Pass by Value Pass by Reference Pass by Result Pass by Value-Result Pass by Name

Pass By Value Make a copy of the value Send the copy to the function Result NOT transmitted back void test(int A) {A++;} //2 void main() { int B=5; //1 test(B); cout << B;//3 } AB //1 //2 // (entry)

Pass By Result No input value Send the copy to the function Result transmitted back on return void test(int A) {A++;} //2 void main() { int B=5; //1 test(B); cout << B;//3 } AB //1 //2 // (entry) ?5 5 ?

Pass By Value Result Copy of input value Use the copy in the function Result transmitted back on return void test(int A) {A++;} //2 void main() { int B=5; //1 test(B); cout << B;//3 } AB //1 //2 // (entry)

Pass By Reference Send address of original Use pointer inside function No need to do explicit return void test(int A) {A++;} //2 void main() { int B=5; //1 test(B); cout << B;//3 } AB //1 //2 // (entry) *B

Pass By Name Conceptual model is to substitute name of the actual parameter for the formal parameter Functions like reference in MOST cases When passing parameters like i,a[i] different results occur

Procedure BIGSUB integer GLOBAL; integer array LIST[1:2]; procedure SUB(PARAM) begin PARAM:=1; GLOBAL:=GLOBAL+1; PARAM:=5; end; begin LIST[1]:= 2; LIST[2]:= 2; GLOBAL :=1; SUB(LIST[GLOBAL]) end; Looks like only 2 changes in the procedure. First assignment to PARAM appears to have no effect! Substitute actual for formal Procedure BIGSUB integer GLOBAL; integer array LIST[1:2]; procedure SUB(PARAM) begin LIST[GLOBAL] :=1; GLOBAL:=GLOBAL+1; LIST[GLOBAL] :=5; end; begin LIST[1]:= 2; LIST[2]:= 2; GLOBAL :=1; SUB(LIST[GLOBAL]) end; Actually updates LIST[1] -> 1 LIST[2] -> 5 and GLOBAL -> 2

Review the examples in Section 8.5.8

2-d arrays as parameters Recall from earlier notes that 2-d arrays are –column major or –row major Formula for accessing elements for row major requires row size in dimension Loc (a[I,J]) = base address (a) (I-lb1)*size of row + (J-lb2)*size element size of row=number columns allocated *size element

Addressing Storage is row-major or column-major order (1,2)(1,1) (2,2)(2,1) (3,2)(3,1) (1,2) (1,1) (2,2) (2,1) (3,2) (3,1) (1,2) (1,1) (2,2) (2,1) (3,2) (3,1) int A[2,3];

C/C++ does row major void fun( int matrix[][10]) { …} void main () { int mat[5][10]; … fun(mat); … } Original dimension 5x10 Parameter only showing number of columns Row major is sized by column dimension. ONLY WORKS IF COLUMN SIZE IS 10!

Other ways of handling 2-d arrays Some languages such as Ada store a run-time property for the dimension float sumer(float mat[][] ) { float sum=0.0; int row; for(row=0;row<mat.length;row++)...