I was solving some problem on codeforces. Normally I first check if the character is upper or lower English letter then subtract or add 32 to convert it to the corresponding letter. But I found someone do ^= 32 to do the same thing. Here it is:

char foo = 'a';
foo ^= 32;
char bar = 'A';
bar ^= 32;
cout 

I have searched for an explanation for this and didn't find out. So why this works?