What are Semantic errors in a programming language?

Answer 1

Semantic or Syntax errors are errors in the way a programmer has written his code. The code does not conform to language standards and is incorrect.

Ex:

for(int i = 0, i++, i<10) {

}

The above is a syntactically incorrect declaration of a for loop in Java. The compiler would not let you compile this code successfully.

Answer 2

A semantic error is one that will not be caught by the compiler (it is not a syntax error), but will produce undesirable or unpredictable results during the execution of the program. For example, a loop that uses "while(x = 5)" will still compile, but will run indefinitely, because x will be set to 5 each time, and any non-zero value will continue a while loop. Assuming x is used within the loop, it would also produce erroneous results.