Change a call-by-value parameter does not affect the argument
#include <iostream>
using namespace std;
double f(double x);
int main()
{
double t = 10.0;
cout << "1/10.0 is " << f(t) << "\n";
cout << "Value of t is still: " << t << "\n";
return 0;
}
double f(double x)
{
x = 1 / x;
cout << "inside f " << x << "\n";
return x;
}inside f 0.1
1/10.0 is 0.1
Value of t is still: 10
Change the contents of an array using a function
#include <iostream>
using namespace std;
void f(int *n, int num);
int main()
{
int i, nums[10];
for(i=0; i < 10; i++) nums[i] = i+1;
cout << "Original contents: ";
for(i=0; i < 10; i++) cout << nums[i] << " ";
cout << "\n";
f(nums, 10); // compute cubes
cout << "Altered contents: ";
for(i=0; i<10; i++) cout << nums[i] << " ";
return 0;
}
void f(int *n, int num)
{
while(num) {
*n = *n * *n ;
num--;
n++;
}
}Original contents: 1 2 3 4 5 6 7 8 9 10
Altered contents: 1 4 9 16 25 36 49 64 81 100
Declare int array parameter for a function without indicating the array length
#include <iostream>
using namespace std;
void display(int num[]);
int main()
{
int t[10], i;
for(i=0; i < 10; ++i) t[i]=i;
display(t); // pass array t to a function
return 0;
}
void display(int num[])
{
int i;
for(i=0; i < 10; i++) cout << num[i] << " ";
}0 1 2 3 4 5 6 7 8 9
Define function to accept three int parameters
#include <iostream>
using namespace std;
void box(int length, int width, int height); // box()"s prototype
int main()
{
box(7, 20, 4);
box(50, 3, 2);
box(8, 6, 9);
return 0;
}
void box(int length, int width, int height)
{
cout << "volume of box is " << length * width * height << "\n";
}volume of box is 560
volume of box is 300
volume of box is 432
Demonstrate the pointer version of swap(): Exchange the values of the variables pointed to by x and y
#include <iostream>
using namespace std;
void swap(int *x, int *y);
int main()
{
int i, j;
i = 10;
j = 20;
cout << "Initial values of i and j: ";
cout << i << " " << j << "\n";
swap(&j, &i); // call swap() with addresses of i and j
cout << "Swapped values of i and j: ";
cout << i << " " << j << "\n";
return 0;
}
void swap(int *x, int *y)
{
int temp;
temp = *x;
*x = *y;
*y = temp;
}Initial values of i and j: 10 20
Swapped values of i and j: 20 10
Function parameter: Use int pointer to accept an array
#include <iostream>
using namespace std;
void display(int num[]);
int main()
{
int t[10], i;
for(i=0; i < 10; ++i) t[i]=i;
display(t); // pass array t to a function
return 0;
}
void display(int *num)
{
int i;
for(i=0; i < 10; i++) cout << num[i] << " ";
}0 1 2 3 4 5 6 7 8 9
Handling an array parameter as a pointer
#include <iostream>
using std::cout;
using std::endl;
double average(double* array, int count);
int main() {
double values[] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0};
cout << "Average = "<< average(values, (sizeof values)/(sizeof values[0]))<< endl;
return 0;
}
double average(double* array, int count) {
double sum = 0.0;
for(int i = 0 ; i < count ; i++)
sum += *array++;
return sum/count;
}Average = 5.5
Pass a pointer to a function.
#include <iostream>
using namespace std;
void f(int *j);
int main()
{
int i;
int *p;
p = &i;
f(p); // pass a pointer
cout << i;
return 0;
}
void f(int *j)
{
*j = 100;
}100
Pass a string to a function: Invert the case of the letters within a string
#include <iostream>
#include <cstring>
#include <cctype>
using namespace std;
void f(char *str);
int main()
{
char str[80];
strcpy(str, "ABCD");
f(str);
cout << str;
return 0;
}
void f(char *str)
{
while(*str) {
if(isupper(*str))
*str = tolower(*str);
else if(islower(*str))
*str = toupper(*str);
str++;
}
}abcd
Passing an array to a function
#include <iostream>
using std::cout;
using std::endl;
double average(double array[], int count);
int main() {
double values[] = {1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0};
cout << "Average = "
<< average(values, (sizeof values)/(sizeof values[0]))
<< endl;
return 0;
}
double average(double array[], int count) {
double sum = 0.0;
for(int i = 0 ; i < count ; i++)
sum += array[i];
return sum/count;
}Average = 5.5
Passing a two-dimensional array to a function
#include <iostream>
using std::cout;
using std::endl;
double f(double values[][4], int n);
int main() {
double beans[3][4] = {
{ 1.0, 2.0, 3.0, 4.0},
{ 5.0, 6.0, 7.0, 8.0},
{ 9.0, 10.0, 11.0, 12.0}
};
cout << f(beans, sizeof beans/sizeof beans[0])<< endl;
return 0;
}
double f(double array[][4], int size) {
double sum = 0.0;
for(int i = 0 ; i < size ; i++)
for(int j = 0 ; j < 4 ; j++)
sum += array[i][j];
return sum;
}78
Passing int by value
#include <iostream>
void swap(int x, int y);
int main()
{
int x = 5, y = 10;
std::cout << "Main. Before swap, x: " << x << " y: " << y << "\n";
swap(x,y);
std::cout << "Main. After swap, x: " << x << " y: " << y << "\n";
return 0;
}
void swap (int x, int y)
{
int temp;
std::cout << "Swap. Before swap, x: " << x << " y: " << y << "\n";
temp = x;
x = y;
y = temp;
std::cout << "Swap. After swap, x: " << x << " y: " << y << "\n";
}Main. Before swap, x: 5 y: 10
Swap. Before swap, x: 5 y: 10
Swap. After swap, x: 10 y: 5
Main. After swap, x: 5 y: 10
Pass int array to a function
#include <iostream>
using namespace std;
void display(int num[10]);
int main()
{
int t[10], i;
for(i=0; i < 10; ++i) t[i]=i;
display(t); // pass array t to a function
return 0;
}
void display(int num[10])
{
int i;
for(i=0; i < 10; i++) cout << num[i] << " ";
}0 1 2 3 4 5 6 7 8 9
Pass variable address to a function
#include <iostream>
using namespace std;
void f(int *j);
int main()
{
int i;
f(&i);
cout << i;
return 0;
}
void f(int *j)
{
*j = 100; // var pointed to by j is assigned 100
}100
the use of ... and its support macros va_arg, va_start, and va_end
#include <stdio.h>
#include <stdarg.h>
#include <string>
void vsmallest(char *message, ...);
int main()
{
vsmallest("Print %d integers, %d %d %d",10,4,1);
return(0);
}
void vsmallest(char *message, ...)
{
int inumber_of_percent_ds=0;
va_list type_for_ellipsis;
int ipercent_d_format = "d";
char *pchar;
pchar=strchr(message,ipercent_d_format);
while(*++pchar != "\0") {
pchar++;
pchar=strchr(pchar,ipercent_d_format);
inumber_of_percent_ds++;
}
printf("print %d integers,",inumber_of_percent_ds);
va_start(type_for_ellipsis,message);
while(inumber_of_percent_ds--)
printf(" %d",va_arg(type_for_ellipsis,int));
va_end(type_for_ellipsis);
}Use array as function"s parameter
#include <iostream.h>
float Total(float a[],int num);
const int SIZE = 10;
main()
{
float * f = new float [SIZE];
for (int i=0;i<SIZE;i++)
f[i]=i+i; //*(f+i)
cout <<"Sum = " << Total( f ,SIZE) <<endl;
cout << "Average = " << Total(f,SIZE)/SIZE;
delete []f;
return 0 ;
}
float Total(float a[],int num)
{
int i;
float sum = 0;
for (i=0; i<num ; i++)
sum += a[i];
return sum;
}Sum = 90
Average = 9"
Using reference parameters
#include <iostream>
using std::cout;
using std::endl;
int larger(int& m, int& n);
int main() {
int value1 = 10;
int value2 = 20;
cout << endl << larger(value1, value2) << endl;
return 0;
}
int larger(int& m, int& n) {
return m > n ? m : n;
}20
var args has to be the last one
#include <cstdio>
#include <cstdarg>
#include <iostream>
using namespace std;
bool debug = false;
void debugOut(char* str, ...)
{
va_list ap;
if (debug) {
va_start(ap, str);
vfprintf(stderr, str, ap);
va_end(ap);
}
}
void printInts(int num, ...)
{
int temp;
va_list ap;
va_start(ap, num);
for (int i = 0; i < num; i++) {
temp = va_arg(ap, int);
cout << temp << " ";
}
va_end(ap);
cout << endl;
}
int main(int argc, char** argv)
{
debug = true;
debugOut("int %d\n", 5);
debugOut("String %s and int %d\n", "hello", 5);
debugOut("Many ints: %d, %d, %d, %d, %d\n", 1, 2, 3, 4, 5);
printInts(5, 5, 4, 3, 2, 1);
return (0);
}
