Why does the ouput is

Question

Why does the output of this code is 0 10 10.dosnt the variable v without value in both the first and third cases?

#include <iostream>
using namespace std;
void f(bool val)
{
    int v;
    if(val)v=10;
    cout<<v<<endl;

}
int main() {

    f(false);
    f(true);
    f(false);
    return 0;
}

C++ is probably not like languages you are used to. There are no variables without a value. It just so happens that you can't always know what the value is, or if it's safe to use. — StoryTeller - Unslander Monica, Jun 17 '18 at 05:05
if `val` is false, then print uninitialized `v` will lead to UB. — con ko, Jun 17 '18 at 06:03

score 1 · Answer 1 · answered Jun 17 '18 at 04:34

1

Because when val = false this condition if(val) is not satisfied so the uninitialized variable v will be printed out.

At that time the value of v could be 0, the last value, or anything else. It's undefined.

answered Jun 17 '18 at 04:34

Van Tr

5,889
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20
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score 0 · Answer 2 · answered Jun 17 '18 at 04:29

int v just declares the v variable, but doesn't assign a value to it, so its value is undefined, it will be same as the current value in the memory.

you can assign v an initial value when declare, likes int v = 0, so when val is false, the v will be always 0.

score 0 · Answer 3 · answered Jun 17 '18 at 04:56

Your answer could vary as x 10 x where x can be any number. Actually, it's the garbage value. You will get its different value in different compiler on the different platform.

Somewhere you will get 0 10 10 because it buffers the value of v. but somewhere else will get 10 10 10 because it buffers the value at compile time. So, its not correct to say what will be the value of x.

So, you should say the answer will be x 10 x where x is the garbage value.

Not exactly so. The behavior is undefined so it might do anything. — awesoon, Jun 17 '18 at 05:02

Vidyul Shah · Answer 4 · 2018-06-17T04:45:56.160

-3

The answer will be 10 10 10 You need to compare value of val in the if condition statement to get different answers. It is taking the value of v in the if statement because there is no comparison. Try it some other Compilers.

try here https://www.onlinegdb.com/online_c++_compiler

edited Jun 17 '18 at 04:45

answered Jun 17 '18 at 04:41

Vidyul Shah

1
1

Always add some explanation to your answer. – Rajat Jain Jun 17 '18 at 04:44
The values could have been anything because it's undefined behavior. This shows nothing. – eesiraed Jun 17 '18 at 04:45
3

Your answer is wrong. The OP is actually comparing `val` in the `if` statement – awesoon Jun 17 '18 at 04:47
The condition of an if statement doesn't have to be a comparison. It can be anything that is or can be converted to a bool value. – eesiraed Jun 17 '18 at 04:47

Why does the ouput is

4 Answers4