函数式编程 - 按值调用

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定义函数后，我们需要将参数传递给它以获得所需的输出。大多数编程语言支持按值调用和按引用调用方法将参数传递给函数。

在本章中，我们将学习“按值调用”在面向对象编程语言（如 C++）和函数式编程语言（如 Python）中的工作原理。

在按值调用方法中，原始值无法更改。当我们将参数传递给函数时，它由函数参数本地存储在堆栈内存中。因此，这些值仅在函数内部更改，不会对函数外部产生影响。

C++ 中的按值调用

以下程序显示了 C++ 中按值调用的工作原理 -

#include <iostream> 
using namespace std; 

void swap(int a, int b) {    
   int temp; 
   temp = a; 
   a = b; 
   b = temp; 
   cout<<"\n"<<"value of a inside the function: "<<a; 
   cout<<"\n"<<"value of b inside the function: "<<b; 
}  
int main() {     
   int a = 50, b = 70;   
   cout<<"value of a before sending to function: "<<a; 
   cout<<"\n"<<"value of b before sending to function: "<<b; 
   swap(a, b);  // passing value to function 
   cout<<"\n"<<"value of a after sending to function: "<<a; 
   cout<<"\n"<<"value of b after sending to function: "<<b; 
   return 0;   
}  

它将产生以下输出 -

value of a before sending to function:  50 
value of b before sending to function:  70 
value of a inside the function:  70 
value of b inside the function:  50 
value of a after sending to function:  50 
value of b after sending to function:  70 

Python 中的按值调用

以下程序显示了 Python 中按值调用的工作原理 -

def swap(a,b): 
   t = a; 
   a = b; 
   b = t; 
   print "value of a inside the function: :",a 
   print "value of b inside the function: ",b 

# Now we can call the swap function 
a = 50 
b = 75 
print "value of a before sending to function: ",a 
print "value of b before sending to function: ",b 
swap(a,b) 
print "value of a after sending to function: ", a 
print "value of b after sending to function: ",b 

它将产生以下输出 -

value of a before sending to function:  50 
value of b before sending to function:  75 
value of a inside the function: : 75 
value of b inside the function:  50 
value of a after sending to function:  50 
value of b after sending to function:  75