Program Efficiency & Readability [closed] - c++

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I want to know which program will be more efficient (memory usage) and why? The first program has lesser variables but more computations. Can you really say? All the program does is find the largest of 3 numbers.
#include <iostream>
using namespace std;
int max(int num1, int num2, int num3) {
if((num1 > num2) && (num1 > num3)) {
return num1;
} else if((num2 > num1) && (num2 > num3)) {
return num2;
} else {
return num3;
}
}
int main() {
int num1, num2, num3;
cout << "Enter first number" << endl;
cin >> num1;
cout << "Enter second number" << endl;
cin >> num2;
cout << "Enter third number" << endl;
cin >> num3;
cout << "Maximum value: " << max(num1, num2, num3) << endl;
return 0;
}
OR
#include <iostream>
using namespace std;
int maximum(int num1, int num2, int num3) {
int largest;
if (num1 > num2) {
largest = num1;
} else {
largest = num2;
} if (num3 > largest) {
largest = num3;
} return largest;
}
int main() {
int number1, number2, number3, max;
cout << "Enter the first number: ";
cin >> number1;
cout << "Enter the second number: ";
cin >> number2;
cout << "Enter the third number: ";
cin >> number3;
max = maximum(number1, number2, number3);
cout << "The maximum value is " << max << endl;
return 0;
}
Also, I want to know if it is bad to give the same variable names in the main() and the max() functions? (In program 1)

Answer 1

Inspect the assembly of an optimizing compiler to reach a conclusion
See e.g. this on godbolt.com ¹
The other on godbolt too: ¹
Looks like maximum is more efficient using these optimization flags on GCC
¹ appears the godbolt permalinks might not be working. It's easy to paste the snippets yourself. I use rand() and return to avoid the compiler optimizing it all out

Answer 2

There are different flavors of efficiency. One program can make more efficient use of memory, while another executes faster. So the first step is to be more precise on the type of efficiency you are after.
That said, a few bytes here and there are just not even worth considering on virtually all computer platforms. So simplifying the code to run faster, even if a little more memory is used, is generally a good approach.
There is no problem with using the same variable names in different functions, unless they cause confusions.

Answer 3

It is best to go down the avenue of writing readable code in the first instance.
If performance is an issue the do some analysis. Always remember the 80/20 rule http://en.wikipedia.org/wiki/Pareto_principle
So to answer your question I do not know as it depends on the OS/compiler options.

Answer 4

I would personally write it like this:
int max(int a, int b)
{
return (a > b ? a : b);
}
int main()
{
int number1, number2, number3;
cout << "Enter the first number: ";
cin >> number1;
cout << "Enter the second number: ";
cin >> number2;
cout << "Enter the third number: ";
cin >> number3;
cout << "The maximum value is " << max(number1, max(number2, number3)) << endl;
return 0;
}

Answer 5

The 2nd algorithm, except for the "double", is bound to be faster because is uses less conditional branches - always 2, while the 1st algorithm needs at least 2 conditional branches, and sometimes more.
You might consider to omit an assignment:
int max(int num1, int num2, int num3) {
if(num1<num2) num1=num2;
if(num1<num3) num1=num3;
return num1;
}