Simple C program labelled as virus - c

Question

I was writing a program to input a string and output alternate characters in the string and I could compile it once, and building it made my antivirus program report that it is a virus (Gen:variant.graftor.74557).
Does any of my code causes something malicious to be called a virus
#include<stdio.h>
#include<string.h>
void altchar()
{
char a[50];
printf("Enter a string");
gets(a);
int i=0;
for(i=0;i<strlen(a);i+=2)
printf("%c",*(a+i));
}
int main()
{
altchar();
return 0;
}
Other c programs compiles very smoothly with no clashes with my AV.
Update:
My AV has no problem with gets() function, and other programs that use gets works smoothly.
Update 2:
By the way, I can run the program exactly once, then it is moved to quarantine.
And the output is nothing and the compiler tells me
Process returned 1971248979 (0x757EDF53) execution time: -0.000 s
For curious minds, I use Bitdefender Antivirus!

Answer 1

The "virus" detected is actually a placeholder name for the F-Secure generic trojan detector. It looks into programs for suspect behaviour. Unfortunately that kind of analysis is bound to sometimes producing false positives.
Maybe your harmless code matches some known malware behaviour on a byte code level? Try making a small change to your code and see if the problem goes away. Otherwise you can submit your program (info on the paged linked above) as a false positive to help them improve their database.

Answer 2

The classic methodology of an antivirus software is to take a few bytes (very well chosen bytes) from an infected file and use those as an identifier string ... it searches the executables and if the bytes match with some bytes from an executable (this check is most of the time done when opening (running) an executable, or when performing a full system scan) then it marks it as a virus.
Fix your code (as per comments), and recompile ... see what happens :)