procedure trouverPosition( int A[*], int n, int v ) returns int pos
# PRECONDITION
#    n >= 1,
#    ALL( 1 <= i < n :: A[i] <= A[i+1] )
# POSTCONDITION
#    SOME( 1 <= i <= n :: A[i]    = v ) => (1 <= pos <= n) & A[pos] = v,
#    ALL ( 1 <= i <= n :: A[i] ~= v ) => pos = 0
{
  pos = trouverPosRec( A, 1, n, v );
}

procedure trouverPosRec( int A[*], int inf, int sup, int v ) returns int pos
{
  if (inf == sup) {
    if (A[inf] == v) {
      pos = inf;
    } else {
      pos = 0;
    }
  } else {
    int m = (inf+sup)/2;
    if (v <= A[m]) {
      pos = trouverPosRec(A, inf, m, v);
    } else {
      pos = trouverPosRec(A, m+1, sup, v);
    }
  }
}