During the compilation phase, the program data vector is created. The program data vector includes the two automatic variables _N_ and _ERROR_. The descriptor portion of the new SAS data set is created at the end of the compilation phase. The descriptor portion includes the name of the data set, the number of observations and variables, and the names and attributes of the variables. Observations are not written until the execution phase.

Syntax checking can detect many common errors, but it cannot verify the values of variables or the correctness of formats.

The DATA step executes once for each record in the input file, unless otherwise directed.

The remaining variables are initialized to missing. Missing numeric values are represented by periods, and missing character values are represented by blanks.

The default value of _ERROR_ is 0, which means there is no data error. When an error occurs, whether one error or multiple errors, the value is set to 1.

By default, at the end of the DATA step, the values in the program data vector are written to the data set as an observation, control returns to the top of the DATA step, the value of the automatic variable _N_ is incremented by one, and the values of variables that were created in programming statements are reset to missing. The automatic variable _ERROR_ is reset to 0 if necessary.

The order in which variables are defined in the DATA step determines the order in which the variables are stored in the data set.

When SAS cannot detect syntax errors, the DATA step compiles, but it does not execute.

A semicolon is missing from the second line. It will cause an error because the INPUT statement will be interpreted as an invalid INFILE statement option.

The third line of the log displays the value for IDnum, which is clearly a character value. The fourth line displays the values in the program data vector and shows a period, the symbol for a missing numeric value, for IDnum. The other values are correctly assigned. Thus, it appears that numeric values were expected for IDnum. A dollar sign, to indicate character values, is missing from the INPUT statement.