bug795.cpp

1     #include <stdio.h>
2     #define N 6
3     double wind_velocity[N] = { 0.0, 14.1, 5.6, 6.0, 23.3, 15.0 } ;
4     double ave_wind( int n )
5         {
6         int j = 0;
7         double sum = 0.0;
8         for( int i = 1; i <= n; i++ )
9             {
10            sum += wind_velocity[i];
11            j = i;
12            }
13        return wind_velocity[j]/j;
14        }
15    int main()
16        {
17        for( int i = 0; i < N; i++ )
18            printf( "%d %g\n", i , ave_wind(i) );
19        return 0;
20        }

In determining the average wind velocity of the first 5 days of March the programmer made one of those errors that caused a bit of embarrassment during a customer demonstration. What went wrong?

bug795.cpp lint Output

--- Module:   bug795.cpp
                             _
    return wind_velocity[j]/j;
bug795.cpp(13) : Info 795: Conceivable division by 0 [Reference: file bug795.cpp: line 6]
    _
    }
bug795.cpp(14) : Warning 550: Symbol 'sum' (line 7) not accessed

Reference Manual Explanation

 
795   Conceivable division by 0  -- In a division or modulus operation the division is
      deduced to be conceivably 0. See Section 9.2 Value Tracking for the meaning of
      "conceivable".