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I am very new to Algorithms and although i understand its very simple code im finding it difficult to find the loop invariant in the code below. Can someone please explicitly tell me what a good loop invariant for the code below is. Any help is much appreciated 

int sumBetween (int x , int y){
    //pre-condition : x<=y
    //post : returns the sum x+(x+1)+(x+2)+.........+y
    int sum=0;
    for(int i=x; i!=y+1; i++) {
        sum+=i;
    }

I cant think of any loop invariant other than sum equalling all the integers from x to y but that is not true before the first iteration. Is there a loop invariant that covers the post-condition ?

Chris
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1 Answers1

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The loop invariant is that which does not vary from iteration to iteration.

In your case, that's the variable y.

Mike Nakis
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