Programming Essentials in C - Lecture 6

Difference Between Syntax and Semantics

Aspect	Syntax	Semantics
Definition	The set of rules that define the structure and format of code.	The meaning and logic of the code.
Focus	How code should be written (grammar, symbols, structure).	What the code does (its behavior and output).
Errors	Syntax Errors occur when the rules of the language are broken.	Semantic Errors occur when the code runs but gives incorrect results.
Checking	Checked at compile-time (before execution).	Checked at runtime (while the program runs).
Example of Incorrect Usage	int 5num = 10; (Invalid variable name - syntax error).	int a = 5 / 0; (Dividing by zero - semantic error).

Syntax Errors

1. Missing Semicolon:

int x = 5
printf("%d\n", x);

Error: The statement int x = 5 is missing a semicolon at the end. The C compiler expects statements to be terminated by a semicolon.

2. Undeclared Variable:

a = 10;
printf("%d\n", a);

Error: The variable a is used without being declared first. In C, you must declare a variable (specify its type) before you can use it.

3. Mismatched Braces:

int main() {
    printf("Hello\n");
    if (5 > 2) {
      printf("Condition is true\n");
    }
// Missing closing brace for main function

Error: The closing curly brace } for the main function is missing. Braces must be properly opened and closed to define code blocks.

Semantic Errors:

1. Type Mismatch in Assignment:

int num = "hello";

Error: You are trying to assign a string literal "hello" to an integer variable num. The types are incompatible, even though the statement is syntactically correct.

2. Dividing by Zero:

int a = 10;
int b = 0;
int result = a / b;
printf("%d\n", result);

Error: Dividing an integer by zero is a mathematically undefined operation. While the C code is syntactically valid, it leads to undefined behavior or a runtime error.

3. Using printf with Incorrect Format Specifier:

int value = 123;
printf("%s\n", value);

Error: The format specifier %s is used to print a string (a sequence of characters), but value is an integer. This mismatch in the expected data type can lead to incorrect output or a runtime error.