three integers compare

It is good to store that numbers in an array. Just plain C array is good enough and in Objective-C best for performance. To find a minimum you can use this function. Similar for maximum.

int find_min(int numbers[], int N){
    int min = numbers[0];
    for(int i=1;i<N;i++)
        if(min>numbers[i])min=numbers[i];

    return min;
}

If that is just three numbers you can do the comparisons manually for best performance. There is a MIN() and MAX() macro in Cocoa in Foundation/NSObjCRuntime.h. For the maximum, just do:

int m = MAX(myI1, MAX(myI2, myI3));

This may be scaled to more numbers and may be faster than the first approach using loop.