Mixed Type Assignment

When the whole RHS expression of a mixed type assignment statement has been evaluated it has a type, this type must then be converted to fit in with the LHS. This conversion could be either a promotion or a relegation. For example,

• LHS INTEGER; RHS REAL or DOUBLE PRECISION -- the RHS needs relegating to be an INTEGER value. The right hand side is evaluated and then the value is truncated (all the decimal places lopped off) then assigned to the LHS.
• LHS REAL or DOUBLE PRECISION; RHS INTEGER -- the INTEGER needs promoting to become a REAL. The right hand side expression is simply stored (approximately) in the LHS.

For example, as real values are stored approximately,

    REAL a,b; INTEGER i
    a = 3.0; b = 4.0
    i = b - a
    j = -0.9
    a = j

• the result of b - a would be close to 1.0 (it could be 1.0000001 or it could be 0.999999999), thus, due to truncation i could contain either 0 or 1.
• j would be truncated to 0; integers are always formed by truncating towards zero.
• a would be set to (about) 0.000.

As long as care is taken, simple assignment should be trouble free.