Conditional Ternary Operators in C?

[nothereanymore]

I understand the basics of the concept, such as :

x = (y > 8) ? 5 : 4;

Which would return "x" as 4 if "y" is less than 8, and 5 if it is greater than 8, but when you start to nest them, things begin to get confusing for me.

 

Take this for an example:

 

int qty = 45;

double total, u_p = 8.75;

int main() {
	total = qty * u_p *(1.0 - (qty > 50 ? 0.15 : (qty > 20 ? 0.1 : (qty > 10 ? 0.05 : 0.0))));
	return total;
}

This returns 98, even though it should return 354 according to my calculations.

 

I see this as:      total = 45 * 8.75 *(1.0 - 0.1)

 

Why does the compiler return this as 98?

 

Even using printf with a %f specifier throws back some error.

[IgorM]

#include<stdio.h>

int qty = 45;

double total, u_p = 8.75;

void main() {
    total = qty * u_p *(1.0 - (qty > 50 ? 0.15 : (qty > 20 ? 0.1 : (qty > 10 ? 0.05 : 0.0))));
    printf("%f", total);
}

 

I ran it and worked just fine, printing 354.375000

[nothereanymore]

40 minutes ago, IgorM said:

 

#include<stdio.h>

int qty = 45;

double total, u_p = 8.75;

void main() {
    total = qty * u_p *(1.0 - (qty > 50 ? 0.15 : (qty > 20 ? 0.1 : (qty > 10 ? 0.05 : 0.0))));
    printf("%f", total);
}

 

 

I ran it and worked just fine, printing 354.375000

Indeed it does. Switched to another compiler and it worked just fine. Another question though, are you familiar with macros that have arguments?

[reniat]

One thing to consider when it comes to ternarys: They are syntactic sugar meant to provide clean code in some places. If the ternary is hard to read or make things unclear, than you very likely should not use a ternary and instead break the code into if/else statements and intermediate variables that are properly names to make things more legible.

 

99 times out of 10, "better code" is the code that is less complicated and still meets all requirements. "clever" code is almost always a negative unless it serves an actual purpose towards requirements. In other words, I would prefer this same code be written as:

 

int qty = 45;

double total, u_p = 8.75;

double get_modifier(int qty) {
	double mod = 0.0;
	if (qty > 50) {
		mod =  0.15;
	} else if (qty > 20) {
		mod = 0.1;
	} else if (qty > 10) {
		mod = 0.05;
	}
	return 1.0 - mod;
}

int main() {
	total = qty * u_p *get_modifier(qty);
	return total;
}

 

It's a few more vertical space sure, but it's a lot cleaner and easier to add to in the future. Also, the two version compile to nearly the exact same thing, but with a bit of recursion resolution added into the ternary version (at least in the latest MSVC compiler)

[IgorM]

1 hour ago, Noirgheos said:

Indeed it does. Switched to another compiler and it worked just fine. Another question though, are you familiar with macros that have arguments?

not much,  but you do you mean something like this?

 

#include<stdio.h>

int qty = 45;
#define OP(X, Y) X * Y *(1.0 - (X > 50 ? 0.15 : (X > 20 ? 0.1 : (X > 10 ? 0.05 : 0.0))))

double total, u_p = 8.75;

void main() {
    total = OP(qty,u_p);
    printf("%f", total);
}

[nothereanymore]

2 hours ago, reniat said:

One thing to consider when it comes to ternarys: They are syntactic sugar meant to provide clean code in some places. If the ternary is hard to read or make things unclear, than you very likely should not use a ternary and instead break the code into if/else statements and intermediate variables that are properly names to make things more legible.

 

99 times out of 10, "better code" is the code that is less complicated and still meets all requirements. "clever" code is almost always a negative unless it serves an actual purpose towards requirements. In other words, I would prefer this same code be written as:

 

int qty = 45;

double total, u_p = 8.75;

double get_modifier(int qty) {
	double mod = 0.0;
	if (qty > 50) {
		mod =  0.15;
	} else if (qty > 20) {
		mod = 0.1;
	} else if (qty > 10) {
		mod = 0.05;
	}
	return 1.0 - mod;
}

int main() {
	total = qty * u_p *get_modifier(qty);
	return total;
}

 

It's a few more vertical space sure, but it's a lot cleaner and easier to add to in the future. Also, the two version compile to nearly the exact same thing, but with a bit of recursion resolution added into the ternary version (at least in the latest MSVC compiler)

Yeah, I agree. This was mostly meant as a somewhat challenging question posed by my teacher.

 

1 hour ago, IgorM said:

not much,  but you do you mean something like this?

 

 

#include<stdio.h>

int qty = 45;
#define OP(X, Y) X * Y *(1.0 - (X > 50 ? 0.15 : (X > 20 ? 0.1 : (X > 10 ? 0.05 : 0.0))))

double total, u_p = 8.75;

void main() {
    total = OP(qty,u_p);
    printf("%f", total);
}

 

Exactly what I meant!  Thank you.