C++ Tutorial/Function/function parameters

Содержание

1 Change a call-by-value parameter does not affect the argument
2 Change the contents of an array using a function
3 Declare int array parameter for a function without indicating the array length
4 Define function to accept three int parameters
5 Demonstrate the pointer version of swap(): Exchange the values of the variables pointed to by x and y
6 Function parameter: Use int pointer to accept an array
7 Handling an array parameter as a pointer
8 Pass a pointer to a function.
9 Pass a string to a function: Invert the case of the letters within a string
10 Passing an array to a function
11 Passing a two-dimensional array to a function
12 Passing int by value
13 Pass int array to a function
14 Pass variable address to a function
15 the use of ... and its support macros va_arg, va_start, and va_end
16 Use array as function"s parameter
17 Using reference parameters
18 var args has to be the last one

Change a call-by-value parameter does not affect the argument

<source lang="cpp">#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;

}</source>

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

<source lang="cpp">#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++; 
 }

}</source>

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

<source lang="cpp">#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] << " ";

}</source>

0 1 2 3 4 5 6 7 8 9

Define function to accept three int parameters

<source lang="cpp">#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";

}</source>

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

<source lang="cpp">#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;

}</source>

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

<source lang="cpp">#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] << " ";

}</source>

0 1 2 3 4 5 6 7 8 9

Handling an array parameter as a pointer

<source lang="cpp">#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;

}</source>

Average = 5.5

Pass a pointer to a function.

<source lang="cpp">#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;

}</source>

Pass a string to a function: Invert the case of the letters within a string

<source lang="cpp">#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++; 
 }

}</source>

abcd

Passing an array to a function

<source lang="cpp">#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;

}</source>

Average = 5.5

Passing a two-dimensional array to a function

<source lang="cpp">#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;

}</source>

Passing int by value

<source lang="cpp">#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";
}</source>

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

<source lang="cpp">#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] << " ";

}</source>

0 1 2 3 4 5 6 7 8 9

Pass variable address to a function

<source lang="cpp">#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

}</source>

the use of ... and its support macros va_arg, va_start, and va_end

<source lang="cpp">#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);

}</source>

Use array as function"s parameter

<source lang="cpp">#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;

}</source>

Sum = 90
Average = 9"

Using reference parameters

<source lang="cpp">#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;

}</source>

var args has to be the last one

<source lang="cpp">#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);

}</source>

C++ Tutorial/Function/function parameters

Содержание

Change a call-by-value parameter does not affect the argument

Change the contents of an array using a function

Declare int array parameter for a function without indicating the array length

Define function to accept three int parameters

Demonstrate the pointer version of swap(): Exchange the values of the variables pointed to by x and y

Function parameter: Use int pointer to accept an array

Handling an array parameter as a pointer

Pass a pointer to a function.

Pass a string to a function: Invert the case of the letters within a string

Passing an array to a function

Passing a two-dimensional array to a function

Passing int by value

Pass int array to a function

Pass variable address to a function

the use of ... and its support macros va_arg, va_start, and va_end

Use array as function"s parameter

Using reference parameters

var args has to be the last one

Навигация

Персональные инструменты

Пространства имён

Варианты

Просмотры

Ещё

Поиск

С

С++

Навигация

Инструменты