Another algorithm -- same problem

// Store 1 + 2 + 3 + 4 in s

Use invariant s= 0 + 1 + 2 + � + i.

To make it true, use initialization: s= 0; i= 0;

When will s = 1+2+3+4 be true? When i=4.

So, use condition i != 4

Body of loop: Make �progress� by increasing i and changing s to maintain the invariant:

i= i+1; s= s+i;

Loop: s= 0; i= 0;

// Invariant: s = 1+2+3+4

while (i !=4)

{i= i+1; s= s+i;}

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