The stdio.h (Standard Input Output) header file contains declarations for printf(), scanf(), and other input/output functions. It is essential for console I/O operations.

Parentheses have the highest precedence in C. Expressions within parentheses are evaluated first, followed by arithmetic operators, then logical operators, and finally assignment operators.

The break statement exits or terminates the current loop immediately. Option D describes continue (which skips to next iteration), while break actually exits the loop.

In C, 'string' is not a primitive data type. C uses 'char' arrays to represent strings. The valid primitive data types are int, float, double, char, void, and their variants.

Variable 'a' is initialized to 10, 'b' is initialized to 20. When c = a + b, c becomes 10 + 20 = 30. Therefore, printf outputs 30.

In C, the 'const' keyword is used to declare constants. Once a const variable is initialized, its value cannot be changed. Options A, C, and D are not valid C syntax.

The return statement is used to exit a function and return a value (if any) to the calling function. If the function has return type void, no value is returned.

stdio.h (Standard Input/Output header) contains declarations for printf(), scanf(), and other I/O functions.

Both 'const int x = 10;' and 'int const x = 10;' are valid ways to declare constants in C. The const keyword can appear before or after the type.

The * operator is the dereference operator that accesses the value at a memory address. The & operator gets the address of a variable.