Double declaration in 13.14

[Qpido]

I don't quite understand why you defined this in the main part of the file in program 13.14.

Code: (Objective-C)

        void exchange (int *pint1, int *pint2);

This

Code: (Objective-C)

void exchange (int *pint1, int *pint2)
{
    int temp;
    
    temp = *pint1;
    *pint1 = *pint2;
    *pint2 = temp;
}

int main(int argc, const char * argv[])
{

    @autoreleasepool {

        int i1 = -5, i2 = 66, *p1 = &i1, *p2 = &i2;
        
        NSLog(@"i1 = %i, i2 = %i", i1, i2);
        exchange(p1, p2);
        NSLog(@"i1 = %i, i2 = %i", i1, i2);
        exchange(&i1, &i2);
        NSLog(@"i1 = %i, i2 = %i", i1, i2);

Works just a fine as

Code: (Objective-C)

void exchange (int *pint1, int *pint2)
{
    int temp;
    
    temp = *pint1;
    *pint1 = *pint2;
    *pint2 = temp;
}

int main(int argc, const char * argv[])
{

    @autoreleasepool {
        void exchange (int *pint1, int *pint2);
        int i1 = -5, i2 = 66, *p1 = &i1, *p2 = &i2;
        
        NSLog(@"i1 = %i, i2 = %i", i1, i2);
        exchange(p1, p2);
        NSLog(@"i1 = %i, i2 = %i", i1, i2);
        exchange(&i1, &i2);
        NSLog(@"i1 = %i, i2 = %i", i1, i2);

You mention something about this I think earlier in the chapter, but I don't quite get it still.

You say we should put them in a different sheet and just import them, so  "void exchange (int *pint1, int *pint2);" isn't necessary right?

Thanks

Q~

[eagle74]

HI Qpido, I have the same problem as you, I really can't understand why it's declared twice, could it be an error of typing??

...hope someone could help us...

[clouded]

The lesson was about trading pointer objects... but what you guys seem to be confused about is the structure of functions.

Basically this is it:

Code: (Objective-C)

#include <file.names>
//function prototype; <-- not always necessary, depends on compiler

// function declaration
{
     function calculations;
}

// main.m
{
     function(call)
     return 0;
}

The way Qpido put it in his main may work as the function prototype, but i'm not sure...
What I think Qpido is confused about is the difference between a method and a function, very similar, but the differences are encapsulation, privacy, and recursion... it's very important to know the differences between all of these and their uses.

[eagle74]

Hy clouded, thanks for your precious explanation 

I looked back in the test and I saw that the double declaration is used only when function is dealing with pointer, for example program 13.7(block to calculate the nth triangular number) doesn't use it.

is it correct?