c programming

Question

what is the output of the c program given below,
 

#include<stdio.h>
int main()
{
    char pt[]="Gatelecture";
    char qt[]="GATE";
    int i=0;
    for( ;pt[i++]=qt[i++]; );
    printf("%s",pt);
}

 

a. AeEe

b. AaEe

c. aAeE

d. none of the above

Comments

so , no segmentation fault

only undefined behavior for different compiler

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@Minipanda

I am getting" GaTe" as output

And as Arvin said he is getting "AaEelecture" on online compiler so it should be undefined behaviour

As different compiler are showing different output

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Yup

Answer 1

Undefined behavior in C. Answer is compiler dependent.

Hence, the correct answer must be d) None of the above.

Comments

when i=4,

qt[4]='\0' it is copied to pt[4] and retrurns '\0' as return value from the expression ===> 0 in the condition of for loop ===> stop

pt[] = "GATE\0ecture" ====> print GATE

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Didn't get what u r saying. Assignment will always be true unless there r violations or other issues.

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Dev c++ compiler gives the output as : AaEe

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:o

Bt how will the loop stop.

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only increment statement is not given means loop always goes to infinity?

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for(initialization;condition;increment/decrement)

Here the condition is pt[i++]=qt[i++]. He didn't say that the loop will go to infinity because there isn't any increment or decrement operation. He said that the condition will not be False ever so the loop will go on forever.

 

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but after sometimes both array will get NULL

right?

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srestha Can you please check the comments under this post .. there has been some discussion over it..

 

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@turendar

with in a sequence point we incremented i twice therefore it is undefined behavior in C.

@gauravkc, this i want to deliver with my previous comment.

The assignment operator is defined (in C) as returning the value of the variable that was assigned to - i.e. the value of the expression (a=b) is the value of a after the expression has been evaluated.

if you didn't get this,

int a,b,c=5;

a=(b=c);

now check what is the value of a 

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a is having 5.

But what I am saying is, the statement will return true or false depending upon successful or unsuccessful assignment. But assignment here cannot be unsuccessful unless there will be access violation or any other reason.

Is this correct reasoning?

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 the statement will return true or false depending upon successful or unsuccessful assignment

then how you get a=5, according to your approach a=1 or a=0 right?

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No as in.. 0 or non-zero.

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but this statement a=(b=c) always a is assigned to 5 only..... think why this happens then you understood the return value of assignment

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5 is assigned. But it is non-zero, hence considered as true. Which keeps the loop going.

when the loop is running, qt[i] turns out to be 0, then it might halt there or it will never halt

 Is this correct?

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yes.... qt[i]='\0' gives return value as 0 then loop will stop

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But it's non zero. It is just defined as null character. Is \0 stored as 0?

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ASCII values of character returns if you are assigning them the integer right?

ex:- int a='A'; ===> int a=65 (Both are equivalent if the range is <128)

ASCII value of '\0' is 0

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Okk.. I don't know why but my laptop is also showing it will go into infinite loop. I'm using gcc 4.9.2 :/

The answer is compiler dependent I guess.

Thanks for having a detailed conversation :)

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note that, i shows undefined behavior.... therefore i may not assign the value as 4 in your compiler... at 4th index only we have null ===> if you didn't get that index to i, you are in infinite loop

if your compiler shows infinite loop, then print i value in the loop....you should didn't encounter i=4