Programming in 'C' CBCCA3T03

Syllabus topics (RTMNU)

• Design methods
• Programming language
• Translators
• Introduction to C
• C character set and keywords
• Escape sequence
• Constants and variables
• Data types
• Conversion specification
• Input and output statements in C
• Operators and expressions (Arithmetic, Relational, Logical, Assignment, Ternary, Bit Wise and Increment & Decrement Operator)

Design Methods

Definition: A design method is a planned way of solving a problem before writing the program. It breaks the problem into clear steps so that coding becomes easy and errors are fewer.

• Top-down design: start with the main problem and divide it into smaller sub-problems (modules) until each part is simple. Example: a billing program is divided into input, calculation of GST and printing of bill.
• Bottom-up design: first build small, basic modules (like a function to add tax) and then join them to make the full program.
• Modular design: the program is made of independent modules (functions in C). Each module does one job and can be tested separately.
• Structured programming: uses only three control structures – sequence, selection (if/switch) and iteration (loops) – and avoids goto. C supports this style.

Tools of design: (1) Algorithm – step-by-step solution written in simple language; (2) Flowchart – diagram of the algorithm using symbols (oval = start/stop, parallelogram = input/output, rectangle = process, diamond = decision, arrows = flow); (3) Pseudocode – English-like code.

Programming Language and Translators

Programming language: a set of words, symbols and rules used to give instructions to a computer.

• Machine language (low level): only 0s and 1s; directly understood by the CPU; very fast but hard to write.
• Assembly language: uses short codes called mnemonics (ADD, MOV, SUB); needs an assembler.
• High level language: English-like words (C, C++, Java, Python); easy to write and portable; needs a compiler or interpreter.

Translator: a program that converts a program written in assembly or high level language (source code) into machine language (object code).

Assembler converts assembly language into machine code. Other helpers: the linker joins object code with library code, and the loader loads the program into memory for running.

Introduction to C

C was developed by Dennis Ritchie at AT&T Bell Laboratories, USA, in 1972. It came from the earlier languages BCPL and B. The UNIX operating system was written mainly in C. It is called a middle level language because it has high level features and can also work close to hardware.

Features of C:

1. Simple and structured – program is divided into functions.
2. Portable – a C program can run on different machines with little change.
3. Fast and efficient – compiled code runs quickly.
4. Rich library – many built-in functions (printf, sqrt, strlen).
5. Pointers – direct access to memory.
6. Extensible – users can add their own functions.

Basic structure: documentation (comments), link section (#include), definition section (#define), global declarations, main() function, user-defined functions.

C Character Set and Keywords

Character set: the characters allowed in C – letters (A–Z, a–z), digits (0–9), special symbols (+ - * / % = ; , { } ( ) & # etc.) and white spaces (blank, tab, newline).

Keywords: reserved words with a fixed meaning; they cannot be used as variable names. ANSI C has 32 keywords, all in lowercase, e.g. auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while.

Identifiers are names given by the programmer to variables and functions. Rules: start with a letter or underscore, no spaces or special symbols, not a keyword, case-sensitive (total and Total are different).

Escape Sequence

An escape sequence is a backslash (\) followed by a character, used inside strings to represent special (non-printing) characters.

Constants and Variables

Constant: a fixed value that does not change while the program runs. Types: integer constant (25, -100), real/float constant (3.14), character constant ('A'), string constant ("RTMNU"). Symbolic constants are made with #define PI 3.14 or const float rate = 18.0;

Variable: a named memory location whose value can change during execution. It must be declared before use: int qty; float price = 99.50;

Data Types

A data type tells the compiler what kind of value a variable will store and how much memory it needs.

*Size depends on the compiler; use sizeof() to check. Modifiers short, long, signed and unsigned change the range. Derived types: arrays, pointers, functions. User-defined: struct, union, enum, typedef.

Conversion Specification and Input/Output Statements

A conversion specification (format specifier) starts with % and tells printf/scanf the type of data: %d int, %f float, %c char, %s string, %lf double, %ld long, %u unsigned, %o octal, %x hexadecimal, %e exponent form. Width and precision can be given: %8.2f prints a float in 8 places with 2 decimals.

• printf() – formatted output: printf("Total = %d", t);
• scanf() – formatted input; the address operator & is used before variable names: scanf("%d", &t);
• getchar() / putchar() – read/write one character.
• gets() / puts() – read/write a string (gets is unsafe; fgets is preferred).

Operators and Expressions

An operator is a symbol that performs an operation on data (operands). An expression is a combination of operands and operators that gives a value, e.g. a + b * 2.

Pre vs post increment: in ++a the value is increased first and then used; in a++ the old value is used first and then increased. Precedence: * / % are done before + -; brackets have the highest priority.

Likely exam questions

1. (Long, 8/16 marks) What is a translator? Explain compiler, interpreter and assembler. Differentiate between compiler and interpreter.
2. (Long, 8/16 marks) What is an operator? Explain arithmetic, relational, logical, ternary, bitwise and increment/decrement operators in C with examples.
3. (Short, 4 marks) Explain any four escape sequences used in C.
4. (Short, 4 marks) What are data types? List the basic data types of C with their format specifiers.
5. (Short, 4 marks) Differentiate between a constant and a variable with examples.

Syllabus topics (RTMNU)

• Storage class: Automatic, Static, External, Register
• Control statement: If-else
• Looping statements (while, do-while and for loop)
• Switch
• Use of break and continue statements
• Function: Arithmetic and string library function
• User defined functions
• Function definition & declaration
• Function call
• Return statement
• Function arguments
• Use of void
• Types of function
• Function with call by value and call by reference
• Recursion

Storage Class: Automatic, Static, External, Register

Definition: A storage class tells four things about a variable – where it is stored (memory or CPU register), its default initial value, its scope (where it can be used) and its lifetime (how long it stays in memory).

• auto – default for local variables; created when the function starts and destroyed when it ends.
• static – keeps its last value between function calls; useful for counters.
• extern – declares a global variable defined elsewhere (outside all functions or in another file).
• register – requests the compiler to keep the variable in a CPU register for fast access (used for loop counters); the address operator & cannot be used on it.

Output: a is always 1, while s becomes 1, 2, 3.

Control Statement: If-else

Control statements decide the order in which statements run. Decision making statements run a block only when a condition is true.

• Simple if: if (marks >= 40) printf("Pass");
• if-else: one block when true, another when false.
• Nested if: an if inside another if.
• else-if ladder: many conditions checked one after another, e.g. grade A/B/C by marks.

Looping Statements (while, do-while and for loop)

A loop repeats a block of statements until a condition becomes false. Every loop has initialisation, condition and update.

• while loop (entry controlled): condition is checked first; body may run zero times. while (i <= 10) { ...; i++; }
• do-while loop (exit controlled): body runs first, condition is checked at the end; body runs at least once. do { ...; i++; } while (i <= 10); – note the semicolon.
• for loop: initialisation, condition and update in one line: for (i = 1; i <= 10; i++). Best when the number of repetitions is known.

Switch Statement

switch is a multi-way decision statement. It compares the value of an integer or character expression with many case labels and runs the matching case. default runs when no case matches. break is needed after each case, otherwise control "falls through" to the next case. Case labels must be constants; float and strings are not allowed.

Use of break and continue Statements

• break – ends the loop or switch immediately; control goes to the statement after the loop.
• continue – skips the remaining statements of the current pass and goes to the next pass of the loop.

Output: Sum = 31 (5 is skipped and the loop stops at 9).

Function: Arithmetic and String Library Functions

A function is a self-contained block of code that does a specific task. Library (built-in) functions are ready-made functions given with the compiler; we only include the header file.

User Defined Functions: Definition, Declaration, Call and Return Statement

A user defined function is written by the programmer. Advantages: avoids repeating code, makes the program modular, easy to test and debug, and functions can be reused.

• Function declaration (prototype): tells the compiler the name, return type and arguments before use: int add(int, int);
• Function definition: the actual body: int add(int a, int b) { return a + b; }
• Function call: uses the function: s = add(10, 20);
• return statement: sends a value back to the calling function and ends the function. A function can return only one value.

Function Arguments, Use of void and Types of Function

Arguments are values passed to a function. Actual arguments are written in the call; formal arguments are written in the definition and receive the values. void means "nothing": void show() returns no value, and int read(void) takes no argument.

Call by Value and Call by Reference

Output: after call by value a=5 b=9 (no change); after call by reference a=9 b=5.

Recursion

Recursion is a process in which a function calls itself. Every recursive function must have a base condition to stop, otherwise it runs forever (stack overflow). Uses: factorial, Fibonacci series, sum of digits.

Working: fact(5) = 5 × fact(4) = 5 × 4 × 3 × 2 × fact(1) = 120.

Likely exam questions

1. (Long, 8/16 marks) What is a storage class? Explain automatic, static, external and register storage classes with their storage, default value, scope and lifetime.
2. (Long, 8/16 marks) What is a function? Explain call by value and call by reference with a suitable program. Also explain recursion with the example of factorial.
3. (Short, 4 marks) Differentiate between while and do-while loop.
4. (Short, 4 marks) Explain the switch statement with an example.
5. (Short, 4 marks) Explain break and continue statements with examples.

Syllabus topics (RTMNU)

• Arrays: Declaration
• Referring individual elements
• Entering data in to an array
• Reading data from array
• Array initialization
• Printing of array
• Searching, Sorting and merging of array
• String: String manipulation using string library function
• Pointer: Introduction to pointer
• Pointer and function
• Pointer and structure
• Pointer and array
• Pointer and string
• Dynamic memory allocation: Sizeof(), malloc(), calloc(), realloc(), free()

Arrays: Declaration and Referring Individual Elements

Definition: An array is a collection of elements of the same data type stored in continuous memory locations under one common name. Example: marks of 60 students can be kept in one array instead of 60 variables.

Declaration: data_type array_name[size]; e.g. int marks[5]; reserves space for 5 integers. Each element is referred to by its index (subscript), which starts from 0: marks[0] is the first element and marks[4] the last. Types: one-dimensional (a list) and two-dimensional (a table/matrix, int m[3][4];).

Array Initialization

• int a[5] = {10, 20, 30, 40, 50}; – all values given.
• int a[] = {1, 2, 3}; – size is taken as 3 automatically.
• int a[5] = {1, 2}; – remaining elements become 0.
• char name[] = "Ram"; – string initialization (4 bytes with \0).

Entering Data into an Array, Reading Data from Array and Printing of Array

A for loop is used to visit each index one by one: scanf with &a[i] enters data, and a[i] inside an expression or printf reads/prints it.

Searching

Searching means finding whether a given value (key) is present in an array and at which position.

• Linear search: compare the key with every element from first to last. Works on unsorted arrays; slow for big arrays.
• Binary search: works only on a sorted array; compare with the middle element and search only the left or right half each time. Much faster.

Output: Found at position 4.

Sorting

Sorting means arranging elements in ascending or descending order. In bubble sort, adjacent elements are compared and swapped if they are in the wrong order; after each pass the largest element moves to the end. Other methods: selection sort, insertion sort.

Output: 10 20 30 40 50

Merging of Array

Merging means joining two arrays into a third array. If both arrays are sorted, we compare their elements and copy the smaller one each time, so the result is also sorted.

Output: 5 10 15 20 25 30 40

String: String Manipulation Using String Library Functions

A string is an array of characters ending with the null character \0. Declared as char city[20]; Read with scanf("%s", city) (stops at a space) or fgets/gets. The header string.h gives functions: strlen (length), strcpy (copy), strcat (join), strcmp (compare: 0 if equal, positive or negative otherwise), strncpy, strchr (find a character), strstr (find a substring).

Output: TaxInvoice 10 0

Pointer: Introduction to Pointer

Definition: A pointer is a variable that stores the address of another variable. Declared as int *p; The operator & (address of) gives the address, and * (value at / indirection) gives the value stored at that address.

Advantages: call by reference, efficient handling of arrays and strings, dynamic memory allocation, building data structures like linked lists.

Pointer and Function, Pointer and Structure

• Pointer and function: passing addresses to a function (call by reference) lets the function change the original variables, e.g. swap(&a, &b) with void swap(int *x, int *y). A function can also return a pointer.
• Pointer and structure: a pointer can hold the address of a structure variable. Members are accessed with the arrow operator ->: struct item it = {101, 250.5}, *p = &it; printf("%d", p->code); Here p->code is the same as (*p).code.

Pointer and Array, Pointer and String

The name of an array is the address of its first element, so p = a; makes p point to a[0]. Then *(p + i) is the same as a[i] (pointer arithmetic: p + 1 moves to the next element, not the next byte). A character pointer can point to a string and move through it until \0.

Output: 10 20 30 40 RTMNU

Dynamic Memory Allocation: sizeof(), malloc(), calloc(), realloc(), free()

Dynamic memory allocation means getting memory while the program is running (run time) instead of fixing it at compile time. It avoids waste of memory. The functions are in stdlib.h; memory comes from the heap.

Output: 10 20 30 40 50

Likely exam questions

1. (Long, 8/16 marks) What is an array? Explain declaration, initialization, entering and printing of a one-dimensional array. Write a C program to sort an array in ascending order using bubble sort.
2. (Long, 8/16 marks) What is a pointer? Explain pointer and array, pointer and string and pointer and structure with examples.
3. (Short, 4 marks) Write a C program for linear search in an array.
4. (Short, 4 marks) Explain any four string library functions with examples.
5. (Short, 4 marks) Differentiate between malloc() and calloc().

Syllabus topics (RTMNU)

• Structure: Declaration structure
• Initializing structure
• Structure variables
• Accessing structure elements
• Arrays of structure
• Array within structure
• Unions: Concept and applications
• Files: Concept of file
• Modes of files
• Open and close
• Creation and reading of files
• Character input/output function
• Formatted input/output function
• String input and output: sscanf, sprintf, gets, puts
• File input/output: fprintf, fscanf, getc, putc
• Block read/write: fread, fwrite
• Random access to files
• Other file function
• Command line argument

Structure: Declaration, Initializing, Structure Variables and Accessing Elements

Definition: A structure is a user-defined data type that groups variables of different data types under one name. Example: a student record has roll number (int), name (char array) and marks (float).

• Declaration: struct student { int roll; char name[20]; float per; }; – this only creates a template; no memory is given yet.
• Structure variables: struct student s1, s2; – memory is allocated now (total of all members).
• Initializing: struct student s1 = {1, "Asha", 82.5}; – values in the same order as members.
• Accessing elements: with the dot (.) operator – s1.roll, s1.per; with a pointer, the arrow (->) operator.

Arrays of Structure and Array within Structure

An array of structures stores many records of the same type, e.g. struct student s[60]; for a whole class; s[i].roll is the roll of the i-th student. An array within a structure means a member itself is an array, e.g. float marks[3]; inside struct student.

Output: 1 Asha Total=240 and 2 Ravi Total=195.

Unions: Concept and Applications

Definition: A union is a user-defined data type like a structure, but all its members share the same memory location. Its size equals the size of its largest member, and only one member can hold a value at a time.

Output shows union size 4 bytes and structure size 12 bytes (on a typical compiler, including padding).

Applications of union: saving memory in embedded systems, storing a value that can be of different types at different times (e.g. a payment that is either cash amount or cheque number), and handling hardware registers.

Files: Concept of File and Modes of Files

File: a named collection of related data stored permanently on a disk. Data in variables is lost when the program ends; a file keeps it. In C a file is handled through a pointer of type FILE * (defined in stdio.h). Types: text files (readable characters) and binary files (data stored as in memory).

Open and Close, Creation and Reading of Files

fp = fopen("stock.txt", "w"); opens a file and returns a FILE pointer, or NULL if it fails. fclose(fp); closes it and saves the buffered data. A file is created by opening it in "w" mode and writing to it, and read by opening it in "r" mode.

Character, Formatted and String Input/Output Functions

Output: "Bill No 15 Amount 1180.00" and "Soap 12". (The syllabus writes "sprint" and "facanf"; these mean sprintf and fscanf.)

Block Read/Write: fread, fwrite

fwrite(ptr, size, n, fp) writes n blocks (records) of given size from memory to a binary file; fread(ptr, size, n, fp) reads them back. They are used to store whole structures (records) at once.

Random Access to Files and Other File Functions

Random access means jumping directly to any position in a file without reading from the start. Functions: fseek(fp, offset, origin) moves the file pointer (origin SEEK_SET = beginning, SEEK_CUR = current position, SEEK_END = end); ftell(fp) gives the current position in bytes; rewind(fp) goes back to the start. Other functions: feof(fp) checks end of file, ferror(fp) checks errors, remove("a.txt") deletes a file, rename(old, new) renames it.

Output: id=3 salary=35000 pos=24 (each record is 8 bytes on a typical compiler).

Command Line Argument

Command line arguments are values given to a program when it is run from the command prompt. main is written as int main(int argc, char *argv[]): argc (argument count) is the number of arguments including the program name, and argv (argument vector) is an array of strings holding them. argv[0] is the program name.

Running show sales 2025 gives argc = 3, argv[1] = sales, argv[2] = 2025. Use: passing file names to a copy program, giving options to a program.

Likely exam questions

1. (Long, 8/16 marks) What is a structure? Explain declaration, initialization and accessing of structure elements. Write a program using an array of structures to store and print records of students.
2. (Long, 8/16 marks) What is a file? Explain the modes of opening a file and the functions fopen, fclose, fprintf, fscanf, fread, fwrite and fseek with examples.
3. (Short, 4 marks) Differentiate between structure and union.
4. (Short, 4 marks) What are command line arguments? Explain argc and argv.
5. (Short, 4 marks) Explain sprintf() and sscanf() with examples.