Of course it is right what you say at the beginning, and C logical operator && and || are what you usually use to "connect" conditions (expressions that can be evaluated as true or false); the comma operator is not a logical operator and its use in that example makes no sense, as explained by other users. You can use it e.g. to "concatenate" statements in the for itself: you can initialize and update j altogether with i; or use the comma operator in other ways
#include <stdio.h>
int main(void) // as std wants
{
int i, j;
// init both i and j; condition, we suppose && is the "original"
// intention; update i and j
for(i=0, j=2; j>=0 && i<=5; i++, j--)
{
printf("%d ", i+j);
}
return 0;
}