📖 1. Introduction to C Programming

C is a general-purpose, procedural programming language used to write programs as a series of steps and functions. It also lets programmers work directly with memory and bits.

C source file (.c)
      ↓
Preprocessing
      ↓
C source after directives are handled
      ↓
Compilation
      ↓
Assembly / object code
      ↓
Linking with required libraries and object files
      ↓
Executable program
      ↓
Operating system loads it
      ↓
Running process

C was developed at Bell Labs in the early 1970s, primarily by Dennis Ritchie, during the development of the Unix operating system.

The name “Dennis Ritchie” is useful to remember, but also understand why C was developed. Programmers needed functions and other features to organise large programs, along with access to memory and hardware for system software.

Higher-level programming ideas          Machine-oriented control
        │                                      │
        │   functions, loops, structures      │
        └─────────────── C ────────────────────┘
                         │
                 pointers, bits,
                 memory, addresses

That balance is why C is sometimes called a “middle-level language” in textbooks. This is an informal description, not an official classification in the C standard.

C helps you understand how programs use data and memory. For example, arrays store related values, while pointers let you work with addresses. These ideas are useful when you later learn data structures and system software.

#include <stdio.h>

int main(void)
{
    printf("Hello, CodeBhavya!\n");
    return 0;
}

#include <stdio.h>     → make I/O declarations available
        ↓
int main(void)         → define the starting function
        ↓
{                      → begin function body
        ↓
printf(...)           → perform output
        ↓
return 0;              → finish successfully
        ↓
}                      → end function body

A compiler, linker, library, and header have different roles. The table below shows how each one helps build a program.

A common C build process has four stages. One command may perform all four, so you do not always see the intermediate files. Running the finished program is a separate step.

program.c
   │
   ├── Preprocessor ──→ expanded source
   │
   ├── Compiler ──────→ assembly/object representation
   │
   ├── Assembler ─────→ object file
   │
   └── Linker ────────→ executable
                              │
                              ↓
                     Operating system
                              │
                              ↓
                       Running process

When a program fails, first ask “At what stage did it fail?” This is much better than changing random lines.

Does it compile?
      │
      ├── No → inspect syntax/types/translation diagnostics
      │
      └── Yes
           ↓
      Does it link?
           │
           ├── No → inspect missing definitions/libraries
           │
           └── Yes
                ↓
          Does it run correctly?
                │
                ├── No → inspect runtime behavior
                │
                └── Yes, but wrong answer → inspect logic

The C standard defines the language and standard library. Compilers may also provide extra features that are not part of standard C.

Read a short program one part at a time. Identify its data, input, calculations, decisions, and output using the cards below.

INPUT
  ↓
PROCESSING
  ↓
DECISION / LOOP
  ↓
OUTPUT
  ↓
CLEANUP (when resources require it)