Modular Programming II

1. Modular Programming II • Functions with single output • Functions with multiple outputs • Concepts of pointers • Multiple calls to a function with in/output parameters • Scope of variables • Formal output parameters as actual arguments • Programming with multiple functions

2. Example of functions with one output value #include <stdio.h> int max(int,int); int min(int,int); Int main(void) { int a, b, c, x1, x2, x3; scanf("%d%d%d", &a, &b, &c); x1 = max(a, b); x2 = min(a, b); if (c >= x1) { x3 = x2; x2 = x1; x1 = c; } else if (c >= x2) { x3 = x2; x2 = c; } else x3 = c; printf("%d, %d, %d", x3,x2,x1); } int max(int x, int y) { int z; if (x > y) z = x; else z = y; return (z); } int min(int x, int y) { int z; if (x < y) z = x; else z = y; return (z); } When max(a,b) is called during the execution of the main program. • It creates two new memory locations for x and y • It pass the values of a and b to x and y respectively • Compute the max • Pass the max value to the main program to assign it to x1 • Release thememory for x and y

3. Functions with multiple outputs • Problem: design a function to output the sign, whole number magnitude, and the fractional part of a floating number • Analysis: the function should have the floating number num as a parameter. It should output the sign, magnitude, and fraction part. Sign is “-” if num <0,sign is “ “ if num = 0; magnitude = the absolute value of num; fraction = num – floor of num;

4. Program That Calls a Function with Multiple Output Arguments

5. Program That Calls a Function with Output Arguments (cont’d)

6. Diagram of Function separate with Multiple Results Parameter Correspondence for separate(value, &sn, &whl, &fr);

7. Concepts of Pointers • The pointer of a variable means the address of the variable. It is the address of the first memory cell of the variable. • If sn is a char variable, then the address of sn is &sn. • The number of bits of a pointer varies depending on machine. For 32 bits processor, it uses four memory cells. • A variable can be defined to hold the pointer of a variable. Such kind of variable is called pointer variable. • Declaration char *signp tells the compiler that signp is a pointer variable, which will contain the address of a type char variable. i.e., signpis a pointer to a char variable. • For char pointer signp, the character stored in the memory cell pointed by signp can be derived by *signp • The unary operator * is called an indirection operator

8. Concepts of Pointers (cond’d) Examples char sn = ‘a’; /* declare a character variable */char *signp; /* declare a char pointer variable */signp = &sn; /* assign the address of sn to signp */printf(“%c”, *signp); /* equivalent to printf(“%c”, sn); */ • A pointer variable must point to a variable of the type it declared char sn = ‘a’; /* declare a character variable */ double *d; /* declare a pointer of double variable */d = &sn; /* this is a wrong assignment! */

9. Example of Pointers #include <stdio.h> main)() { int a = 100, b = 10; int *pointer1, *pointer2; pointer1 = &a; pointer2 = &b; printf(“%d, %d\n”,a, b); printf(“%d, %d\n”,*pointer1, *pointer2); } The output will be 100,10 100,10

10. p1 a &a 5 p p2 b &b 9 p1 a &b 5 p p2 b &a 9 Example • Input two integers a and b, compare and display them in decreasing order #include <stdio.h> main() { int *p1, *p2, *p, a, b; scanf("%d,%d", &a,&b); p1 = &a; p2 = &b; if (a < b) { p = p1; p1 = p2; p2 = p; } printf("\na=%d , b=%d\n", a, b); printf("max = %d, min = %d\n",*p1, *p2); } Input: 5, 9 Display: a = 5, b =9 max = 9, min = 5