Find the output of a C program [closed] - c

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I have been trying solve this question but unable to understand.
If the following program (myprog) is run from the command line as:
myprog friday tuesday sunday
What would be the output?
#include<stdio.h>
int main(int argc, char *argv[]){
while(sizeof argv)
printf("%s",argv[--sizeof argv]);
return 0;
}
The output is-
sunday tuesday friday myprog
Please explain me the output.
Thanx :-)

Answer 1

I am guessing you really what this. It just prints the command line argument out backwards.
#include<stdio.h>
int main(int argc, char *argv[])
{
while (argc)
printf("%s ", argv[--argc]);
printf("\n");
return 0;
}

Answer 2

Disregarding the --sizeof issue, I'm assuming you want to know about the elements of argv.
It contains the arguments and the name of the program. Read any manual or document describing argv.

Answer 3

There are two issues in your code:
--sizeof argv is illegal. It would result in an error.
while(sizeof argv) will result in an infinite loop as the condition will always be true
So in short the code will not compile and will result in an error.

Answer 4

You probably want to understand command line argument processing in C. When you are given some list of program arguments, for example,
myprog friday tuesday sunday
The C language provides arguments to the main() function which provide the number of arguments (4 in this case), and an array of char* (pointers) to these arguments.
Note that sizeof argv is computed at compile time, and the value is the size of a pointer on your system (4 or 8).
First, we explain the arguments to the main function,
int main(
int argc, //an integer count of the number of arguments provided to the program
char* argv[] //an array of pointers to character arguments
)
Your main function is then defined to (apparently) print out the arguments starting at the rightmost argument and working back to the zero-th argument,
{
int argv_sizeof = argc; //you cannot use sizeof argv the way you specified
//argv_sizeof = 4 in your example, but argv[4] is not valid
//argv_sizeof has a value that is one past the rightmost element of argv[]
while( argv_sizeof ) //use argv_sizeof > 0 here; argv_sizeof is 4,3,2,1,0
//when argv_sizeof reaches 0, the while loop terminates
{
printf("%s",argv[--argv_sizeof]); //here you pre-decrement argv_sizeof (3,2,1,0)
//then use argv_sizeof to index into argv[]
//then you print the string at argv[3], argv[2], argv[1], argv[0]
}
//argv_sizeof = 0 here
return 0; //you return the value 0 from the main function
}

Answer 5

Error:
lvalue required as decrement operand
It does not compile.
sizeof is an operator just like + or % and it gives you the size of an object. So, you can't decrement it. Just as somehting like this wouldn't make any sense: --%
The gist of the question is:
What happens if the input is: myprog friday tuesday sunday
When the code does:
index = lastIndex
while(index) // note: while(0) == false
print(array[--index])
So, the output would be the reversal of the elements:
sunday tuesday friday