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ABAP Keyword Documentation → ABAP Programming Guidelines → Robust ABAP →Assignments, Calculations, and Other Types of Data Access
An assignment passes the content of a data object, a return value, or a result of a calculation expression to a data object. If the data types are compatible, the content is copied unchanged. If the data types are incompatible and there is a suitable conversion rule, the content is converted. An assignment is usually performed with the assignment operator (=).
A calculation is executed in a calculation expression, which can be specified in an operand position, in particular on the right side of the assignment operator =. If necessary, the result of a calculation expression is converted to the data type of the operand position or of the result of the assignment. In arithmetic expressions, the calculation is executed in a calculation type based on the data types of all operands including the result.