C Language

What is C?

C is a general-purpose procedural programming language known for its efficiency and close relationship to system-level programming. It is also an excellent way to learn fundamental programming concepts.

• Compiler: Translates C source code into an executable program.
• Header file: Provides declarations for functions and types.
• Function: A reusable block of code that performs a task.
• Use cases: Embedded systems, operating systems, utilities and learning programming fundamentals.

Basic workflow

Write source code → compile it → run the program → test and improve it.

C fundamentals

A C program typically includes header files and a main() function. Statements usually end with semicolons and blocks use braces.

#include <stdio.h>

int main(void) {
    char name[40] = "Ravi";
    int age = 21;
    printf("Hello %s, age %d\n", name, age);
    return 0;
}

Practise variables, integer and floating-point types, characters, operators, conditions and loops. Use the correct format specifiers and validate input.

Functions and modular programming

Functions help split a program into smaller, reusable parts. A function can accept parameters and return a value.

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int main(void) {
    printf("Sum: %d\n", add(4, 6));
    return 0;
}

• Declaration: Tells the compiler the function's name and signature.
• Definition: Contains the function body.
• Parameters: Values passed into a function.
• Recursion: A function calling itself with a stopping condition.

Conditions and loops

Conditions select which statements run, while loops repeat work. Choose a loop that matches the problem and ensure it can terminate.

#include <stdio.h>

int main(void) {
    for (int i = 1; i <= 5; i++) {
        printf("%d\n", i);
    }
    return 0;
}

Practise if/else, switch, for, while and do-while. Watch for off-by-one errors and use braces consistently.

Arrays, strings and pointers

Arrays store multiple values of one type. In C, strings are character arrays ending with the null character '\0'. Pointers store memory addresses.

#include <stdio.h>

int main(void) {
    int score[] = {70, 85, 92};
    int *ptr = score;
    printf("First score: %d\n", *ptr);
    return 0;
}

Practise array indexing, string handling, address-of (&) and dereference (*) operators. Avoid accessing memory outside array bounds.

Structures and user-defined types

Structures group related fields into one record, which is useful for representing entities such as students or products.

#include <stdio.h>

struct Student {
    int id;
    char name[30];
};

int main(void) {
    struct Student s = {101, "Asha"};
    printf("%d: %s\n", s.id, s.name);
    return 0;
}

Explore arrays of structures, nested structures, unions, enumerations and typedef.

Dynamic memory allocation

Dynamic memory functions allow a program to request memory while it runs. Always check allocation results and release memory when finished.

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    int *values = malloc(3 * sizeof *values);
    if (values == NULL) return 1;
    values[0] = 10;
    printf("%d\n", values[0]);
    free(values);
    return 0;
}

Learn malloc(), calloc(), realloc() and free(). Avoid memory leaks, double-free errors and using pointers after freeing memory.

File handling

File I/O lets a C program save data beyond a single run. Check that files open successfully and close them when finished.

#include <stdio.h>

int main(void) {
    FILE *file = fopen("notes.txt", "w");
    if (file == NULL) return 1;
    fputs("Practise C every day.\n", file);
    fclose(file);
    return 0;
}

Practise fopen(), fclose(), fprintf(), fscanf(), fgets() and fputs(), along with file modes and error handling.

Testing and project workflow

1. Write clear requirements and break work into functions.
2. Compile with warnings enabled and fix errors.
3. Test typical inputs, boundary values and invalid inputs.
4. Use a debugger to inspect variables and execution flow.
5. Document how to compile, run and test the program.

Prefer readable code, validate user input and keep memory ownership clear.

C Language glossary