Functions, Memory Layout - stack, and Arrays

Definging Functions

return_type function_name (parameter list)
{
				body of the function
}

• The return_type is the type the function returns
• Some functions do not return values, in this case void is used
• The function name and the parameter list together constitute the function signature
• a function may contain no parameters
• The function body contains a collection of statements that define what the function does

call by value

• The call by value method of passing arguments to a function copies the actual value of an argument into the formal parameter of the function
• changes made to the parameters inside the function have no effect on the arguments

void swap (int x, int y);
int main (){
		int a = 100, b = 20;
		printf("Before swap, value of a : %d\n", a);
		printf("Before swap, value of b : %d\n", b);
		swap(a,b);
		printf("After swap, value of a : %d\n", a ); 
		printf("After swap, value of b : %d\n", b );
		return 0;
}
void swap (int x, int y) {
		int temp = x;
		x = y;
		y = temp;
}

call by reference

• The call by reference method of passing arguments to a function copies the address of an argument into the formal parameter
• Inside the function, the address is used to access the actual argument used in the call
  • changes made to the parameter affect the passed argument
  • To pass by reference, argument pointers are passed to the functions just
• the function parameters need to be declared as pointer types

void swap (int *x, int *y);
int main (){
		int a = 100, b = 20;
		printf("Before swap, value of a : %d\n", a);
		printf("Before swap, value of b : %d\n", b);
		swap(&a,&b);
		printf("After swap, value of a : %d\n", a ); 
		printf("After swap, value of b : %d\n", b );
		return 0;
}
void swap (int *x, int *y) {
		int temp = *x;
		*x = *y;
		*y = temp;
}

Memory Layout - Stack

• The stack segment is the area where local variables are stored
  • local variable are declared in every function including main() in C program
• When we call any function a stack frame is created
• function returns, stack frame is destroyed including all local variables of that particular function
• Stack frame contain some data like return address, arguments passed to the function, local variables,. . .
• A “stack pointer (SP)” keeps track of stack by each push and pop operation onto it

Arrays

• Array a fixed-size sequential collection of elements of the same type
• An array is used to store a collection of data of the same type
• All arrays consist of contiguous memory locations
  • The lowest address corresponds to the first element and the highest address to the last element
• Declaring arrays: double balance[10];

Initialingzing arrays:

double balance[5] = {1000.0, 2.0, 3.4, 17.0, 50.0};

we can ommit the size:

double balance[] = {1000.0, 2.0, 3.4, 17.0, 50.0};

Accessing an array:

balance[4] = 50.0;
double salary = balance[3];

Two-dimensional Arrays

• The simplest form of multidimensional array is the two-dimensional array
• A two-dimensional array is an array of one-dimensional arrays
• Declaring 2D arrays:

int a[3][4];

• Initializing 2D arrays:

int a[3][4] = {
		{0, 1, 2, 3} ,
		{4, 5, 6, 7} , {8, 9, 10, 11}
};

three ways to pass an array to functions

• as a pointer:

void myFunction(int *param) {...}

• as a sized array:

void myFunction(int param[10]) {...}

• as a unsized array:

void myFunction(int param[]) {...}