CSS Computer Science (Optional) — Paper-I, Section-A, Topic II subtopic. How a typical C/C++ program is organized, and the data types available to it.

Anatomy of a Program (C/C++)

#include <stdio.h>      // 1. Preprocessor directives
#define MAX 100          //    (headers, macros)

int globalCount = 0;     // 2. Global declarations

int square(int n) {      // 3. Function prototypes/definitions
    return n * n;
}

int main() {              // 4. main() — program entry point
    int x = 5;             //    local declarations
    x = square(x);         //    statements/processing
    printf("%d", x);       //    output
    return 0;               // 5. return — exit status to OS
}

1. Preprocessor directives — #include, #define, processed before compilation
2. Global declarations — variables/constants visible to the whole file
3. Function prototypes and definitions — including main(), the mandatory entry point
4. main() body — local declarations, statements, control flow
5. Return statement — sends an exit status back to the operating system (0 = success by convention)

Data Types

Primitive (built-in) types:

• Type modifiers: signed, unsigned, short, long adjust range/sign (e.g. unsigned int, long long)

Derived/composite types: array, pointer, function

User-defined types: struct, union, enum, class (C++), typedef-based aliases

Variables: Declaration, Scope, Lifetime

• Declaration: int age; binds an identifier to a data type and reserves memory for it
• Initialization: int age = 25; declares and assigns a value in one step
• Scope — where in the code a variable name is visible: local (inside a function/block) vs global (whole file/program)
• Lifetime — how long a variable's memory persists: automatic (created/destroyed with each function call, default for locals) vs static (persists for the entire program run) vs dynamic (programmer-controlled via malloc/new and free/delete)

Type Conversion