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int sum(int a, int b) { int s = 0; int k = a; //------------------------------------------------------------ // Every time the program reaches the top of the following loop, // s = the sum of all integers that are greater than or // equal to a and strictly less than k // (So s = a + ... + (k-1).) //------------------------------------------------------------ while(k <= b) { s = s + k; k = k + 1; } return s; }