Unit 1: Algorithm development and C fundamentals

An algorithm is a finite, ordered set of clear steps that solves a problem. A good algorithm has input, output, definiteness, finiteness and effectiveness. A flowchart is a diagram of an algorithm using standard symbols.

Pseudocode is the algorithm written in plain, structured English that looks like code but follows no strict syntax.

• Errors: syntax errors (compiler), linker errors (missing functions), run-time errors (division by zero), logical errors (wrong output).
• Debugging: reading error messages, printing intermediate values, dry runs with trace tables, using a debugger (gdb, IDE breakpoints).
• Commands: gcc prog.c -o prog then ./prog.

• Character set: letters (A–Z, a–z), digits (0–9), special symbols (+ − × / % ; { } etc.) and white space.
• Identifiers are names given to variables, functions and arrays. Rules: start with a letter or underscore, contain only letters, digits and underscores, are case-sensitive, and cannot be a keyword. total_marks is valid; 2sum and float are not.
• Keywords are 32 reserved words with fixed meaning in C, such as int, float, if, else, while, for, return, void, struct, switch.

A variable is a named memory location whose value can change: int age = 18;. A constant is a fixed value: integer (25), real (3.5), character ('x') and string ("SBS"). A symbolic constant gives a constant a name: #define PI 3.14159.

An expression combines operands and operators to produce a value.

• Precedence decides which operator is applied first (for example × and / before + and −); associativity decides the order among operators of equal precedence (mostly left to right).
• Library functions are ready-made functions in header files: sqrt(), pow() in math.h; printf(), scanf() in stdio.h; strlen() in string.h.

c#include <stdio.h>
int main() {
    int a = 10, b = 3;
    printf("Sum = %d\n", a + b);       /* 13 */
    printf("Remainder = %d\n", a % b); /* 1 */
    printf("Bigger = %d\n", (a > b) ? a : b);
    return 0;
}

• Assignment: variable = expression; compound forms +=, −=, *=, /=, %=.
• Formatted I/O: printf and scanf with format specifiers %d, %f, %c, %s, %lf; unformatted I/O: getchar, putchar, gets (unsafe — use fgets), puts.

c#include <stdio.h>
int main(void) {
    int a, b;
    printf("Enter two numbers: ");
    scanf("%d %d", &a, &b);
    int sum = a + b;            /* assignment */
    printf("Sum = %d\n", sum);
    return 0;
}