//8 – 1 function
#include <iostream>
using namespace std;
/*
1.the type of return value:int,float,double,char,string ……
2.function name
3.parameter’s list:this function’s parameters that I need to deliver
4.return the expression(表达式)
返回值类型 函数名(参数列表)
{
函数体（各种要写的编程语句）
return 表达式
}
type function name(parameter list)
{
body of function;
}
*/
int add(int a,int b)
{
int c = a + b;
return c;
}
double add2(int a, int b)
{
int c = a + b; //conversion from ‘double’ to ‘int’, possible loss of data
return c;
}
double add3(int a, int b)
{
int c = a + b; //conversion from ‘double’ to ‘int’, possible loss of data
return c;//this step would not be an error,but there is an unvisable translation
//return (double)c; small to big will not make a problem
}
int add4(int a, int b)
{
return a+b;
}
void printAaddB(int a, int b) //func type is null/void(空)
{
int c = a + b ;
cout << c << endl;
return ; //Don’t need to return a value because it’s function type is null/void
}
int max(int a, int b)
{
if (a > b) {
return a;
}
return b;
//to get the maximum value
//or we can use ternary operator
// return a > b ? a : b;
}
int max2(int a, int b)
{
//or we can use ternary operator
return a > b ? a : b;
}
int main(){
//int ret = add2(1, 7);//conversion from ‘double’ to ‘int’, possible loss of data
double ret = add3(1, 7);//this step would not be an error,but there is an unvisable translation
cout << ret << endl;
return 0;
//int is the main function’s return date type
//0 is the main function’s return value
//main is the function’s name
//()is the function’s parameter
}
//8 – 2 function call
#include <iostream>
using namespace std;
/*
function’s calling have the use of encapsulation(封装)
//黑盒(Blach box):we don’t need to know how to get it
*/
int add(int a, int b) {
return a + b;
//return a – (-b);
}
int max(int a, int b) {
return a > b ? a : b;
}
int sum(int n) {
int ret = 0;
for (int i = 1; i <= n; ++i) {
ret += i;
}
//O(n)
return ret;
//枚举算法
//this method is much more calling than the sum2’s method
}
int sum2(int n) {
return (1+n) * n /2;
//O(1)
}
int main() {
//1.the addition’s call(加法的调用)
int a = add(1, 7);
int b = add(a,9);
int c = add(add(1, 7), 9);
//After made the function, I just need to use, instead of knew the details
cout << b << endl;
cout << c << endl;
//2.the maximum number’s call(最大值的调用)
int d = max(a, b);
//3.to get the sum from 1 to n(求1到n的和)
int n;
cin >> n;
int e = sum2(n);
cout << e << endl;
return 0;
}
//8 – 3 function value transfer
#include <iostream>
using namespace std;
/*
| a | b | | a | | b | |tmp | | a | | b |
| 6 | 9 | | 6 | | 9 | | 6 | | 9 | | 6 |
4 bytes 4 bytes 4 bytes 4 bytes
*/
//function value transfer:transfer some parameters into the function inside, and use it within the function inside
void swap(int a, int b) {
cout << “a = ” << a << endl;
cout << “b = ” << b << endl;
cout << “————-“<< endl;
int tmp = a;
a = b;
b = tmp;
cout << “a = ” << a << endl;
cout << “b = ” << b << endl;
cout << “————-” << endl;
}
int main() {
int a = 6;
int b = 9;
swap(a,b);
//the key point of function value transfer:the value we transfered will only be copied, the origin value is the same address
//the value will be destroied when the function is finished execution
//If you want to swap the original value, you can use the pointer
cout << “a = ” << a << endl;
cout << “b = ” << b << endl;
return 0;
}
//8 – 4 function declaration
#include <iostream>
using namespace std;
//int add(int a, int b);//this is a function declaration
int add(int, int);//we can only write the data type when declarating
void func2(int);//declarating in advance is to prevent error
void func1(int x) {
if (x <= 0) {
return;
}
cout << “func1:” << x << endl;
func2(x-1);
}
void func2(int x) {
cout << “func2:” << x << endl;
func1(x-1);
}
int main() {
int x, y;
cin >> x >> y;
int z = add(x, y);
cout << z << endl;
cout << “———” << endl;
func1(-1);
return 0;
}
int add(int a, int b) {
return a + b;
}
//Place the function in this position, we won’t be able to run the code normally,if we didn’t declarate the function at first