## FoVeOOS'11 Competition: challenge 1, in C

Maximum of an array of integers, in C

**Authors:** Claude Marché

**Topics:** Array Data Structure

**Tools:** Frama-C / Jessie / Why3

**References:** The COST FoVeOOS'11 Competition

see also the index (by topic, by tool, by reference, by year)

/* COST Verification Competition. vladimir@cost-ic0701.org Challenge 1: Maximum in an array Given: A non-empty integer array a. Verify that the index returned by the method max() given below points to an element maximal in the array. */ /*@ requires len > 0 && \valid_range(a,0,len-1); @ ensures 0 <= \result < len && @ \forall integer i; 0 <= i < len ==> a[i] <= a[\result]; @*/ int max(int *a, int len) { int x = 0; int y = len-1; /*@ loop invariant 0 <= x <= y < len && @ \forall integer i; @ 0 <= i < x || y < i < len ==> @ a[i] <= \max(a[x],a[y]); @ loop variant y - x; @*/ while (x != y) { if (a[x] <= a[y]) x++; else y--; } return x; } /* Local Variables: compile-command: "make array_max.why3ml" End: */