C Tutorial Swap example
Introduction to functions in C
Syntax
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Call by Value and call by reference
Swap example

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The classic example of wanting to modify the caller's memory is a swap() function which exchanges two values. Because C uses call by value, the following version of Swap will not work...

 

void Swap(int x, int y) {        // NO does not work int temp;

 

temp = x;

x = y;      // these operations just change the local x,y,temp

y = temp;   // -- nothing connects them back to the caller's a,b

}

 

 

// Some caller code which calls Swap()...

int a = 1;

int b = 2;

Swap(a, b);

 

 

Swap() does not affect the arguments a and b in the caller. The function above only operates on the copies of a and b local to Swap() itself. This is a good example of how

"local" memory such as ( x, y, temp) behaves -- it exists independent of everything else only while its owning function is running. When the owning function exits, its local memory disappears.

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