why is my code not printing the largest number? - c++

Question

#include <iostream>
void isMax(int a, int b, int c, int d) {
int ans1, ans0, x;
a = !b, a = !c, a = !d,
b = !c, b = !d,
c = !d, c = !a;
if (a<b && b>c) { // ans0 starts
if (b > d) {
std::cout << b << std::endl;
}
else {
std::cout << d << std::endl;
}
}
else if (a < b && b < c) {
if (c > d) {
std::cout << c << std::endl;
}
else {
std::cout << d << std::endl;
}
}
//ans1
else if (a > b&& a > c) {
if (a > c&& a > d) {
std::cout << a << std::endl;
}
else if (a > c&& a < d) {
std::cout << d << std::endl;
}
else if (a<c && c>d) {
std::cout << c << std::endl;
}
else if (a < c && c < d) {
std::cout << d << std::endl;
}
else {
std::cout << "invalid numbers ahead." << std::endl;
}
}
std::cout << a << b << c << d << std::endl;
};
int main() {
isMax(3, 4, 6, 5);
return 0;
}
it kind of worked before i added
a = !b, a = !c, a = !d,
b = !c, b = !d,
c = !d, c = !a;
this part but did not work when i give the same values for a,b,c,d that`s why i added that part and now it does not work at all.
What is my mistake here ?
This image shows what i am trying to turn into code. Basically i`m trying to write a function that prints out the largest of four variables.

Answer 1

a != b; is true when a and b are different. What you wrote is a = !b; which is "assign to a the logically negated value of b".
I do not see how such assignment could make any sense here. That's why you get correct results without it and non-sense results when you add that assignments.
PS: Even if you "fix" it by writing a != b; the statement alone will have no effect. I suppose you want to return early or skip some of the later conditions when some input is equal.

Answer 2

From your schema, it should be:
void DisplayMax(int a, int b, int c, int d) {
if (b < a) {
if (c < a) {
if (d < a) {
std::cout << a;
} else { // a <= d
std::cout << d;
}
} else { // b < a <= c
if (c < d) {
std::cout << d;
} else {
std::cout << c;
}
}
} else { // a <= b
if (c < b) {
if (d < b) {
std::cout << b;
} else { // b <= d
std::cout << d;
}
} else { // a <= b <= c
if (c < d) {
std::cout << d;
} else {
std::cout << c;
}
}
}
}
But, as shown in other answer, there is simpler ways.
or with std:
void DisplayMax(int a, int b, int c, int d) {
std::cout << std::max({a, b, c, d});
}

Answer 3

I see a few issues:
Your logic seem over complicated for printing the largest of 4 variables.
The name of the isMax function doesn't reflect what it does.
I don't understand the need for a "invalid numbers ahead" if indeed printing the largest of four integers is intended.
I propose a simpler logic with fewer conditions but another variable on the heap.
#include <iostream>
int largestOf(int a, int b, int c, int d) {
int max = a;
if (b > max)
max = b;
if (c > max)
max = c;
if (d > max)
max = d;
return max;
}
void isMax(int a, int b, int c, int d) {
std::cout << largestOf(a, b, c, d) << std::endl;
}

Answer 4

It's not clear at all what you expect the a = !b, ... to accomplish, so I'm going to ignore that.
I am also going to ignore the existence of std::max since this is clearly an exercise.
Your logic tree makes sense, but you can find a more convenient solution if you bark up a different but similar tree.
Consider the case when a > b, i.e. you know for certain that b is not the maximum.
Instead of continuing with a, now look at only c and d.
If c > d, you know that the maximum is not d, so it must be either a or c.
Likewise, if d > c, the maximum is either a or d.
The same line of reasoning for the case when b > a leads to the following algorithm:
Determine max(a,b).
Determine max(c,d).
The maximum of all four numbers is the maximum of the previous two results.
In code:
void isMax(int a, int b, int c, int d) {
int ans0 = a > b ? a : b;
int ans1 = c > d ? c : d;
std::cout << (ans0 > ans1 ? ans0 : ans1) << std::endl;
}
On a side note, a function whose name begins with "is" usually returns a boolean, and you will find more use for a function that returns the maximum than you will of one that prints it.
You can always print that value later if you want to look at it.
Like this:
int max(int a, int b, int c, int d) {
int ans0 = a > b ? a : b;
int ans1 = c > d ? c : d;
return ans0 > ans1 ? ans0 : ans1;
}

Answer 5

This code is over complicated for something fairly simple. If you're new to programming, I suggest you try using arrays, in that way you can easily decide which number is max.
For example:
void isMax(int a, int b, int c, int d) {
int j[4] = { a,b,c,d };
int max = j[0];
for (int i = 1; i < 4; i++) {
if (j[i] > max){ max = j[i]; }
}
cout << max;
}
This is a better way to do it.