How do you write a program to swap two numbers in COBOL without using a third variable?

Answer 1

Offhand, I don't know that it's possible. Without using a third work variable, one of the two is going to get overwritten. I suppose technically you could do something like use C to directly access a memory field or assembler to store in a register to swap them around without formally defining it as a variable, but that's just semantics - you're still basically using another variable (albeit an unnamed one) to perform the swap.