Core C Language Fundamentals and Practical Programs

Posted on Aug 6, 2026 in Computers

C Program to Find the Largest of Three Numbers

#include <stdio.h>
int main() {
    int a, b, c;
    printf("Enter three numbers: ");
    scanf("%d %d %d", &a, &b, &c);
    if (a >= b && a >= c) {
        printf("%d is the largest.\n", a);
    } else if (b >= a && b >= c) {
        printf("%d is the largest.\n", b);
    } else {
        printf("%d is the largest.\n", c);
    }
    return 0;
}

C Program to Check Positive, Negative, or Zero

#include <stdio.h>
int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (num > 0) {
        printf("%d is Positive.\n", num);
    } else if (num < 0) {
        printf("%d is Negative.\n", num);
    } else {
        printf("The number is Zero.\n");
    }
    return 0;
}

Difference Between Structure and Union

A structure and a union are both user-defined data types in C used to group different data types.

• Memory Allocation: Structure allocates memory for every member. Union allocates memory equal only to its largest member, sharing the space among all variables.
• Accessing Members: In structures, all members can be accessed simultaneously. In unions, only one member holds a valid value at any given time.
• Keyword & Syntax: Defined using struct and union keywords.
• Size Calculation: Size of struct >= sum of sizes of all members. Size of union = size of its largest member.
• Value Alteration: In struct, modifying one member does not affect others. In union, modifying one member overwrites the shared memory.

Relational vs. Logical Operators in C

Operators are symbols that perform operations on variables. Relational operators compare two values, while Logical operators combine multiple conditions.

• Relational Operators: <, >, <=, >=, ==, !=.
• Logical Operators: && (AND), || (OR), ! (NOT).

Conditional Statements and Even/Odd Program

Conditional statements allow a program to execute specific blocks of code based on boolean conditions.

• if Statement
• if-else Statement
• nested if-else Statement
• else-if Ladder
• switch-case Statement

#include <stdio.h>
int main() {
    int num;
    printf("Enter an integer: ");
    scanf("%d", &num);
    if (num % 2 == 0) {
        printf("%d is an EVEN number.\n", num);
    } else {
        printf("%d is an ODD number.\n", num);
    }
    return 0;
}

Control Flow of a Switch Statement

The switch statement is a multi-way decision-making structure that branches execution based on constant integer or character values.

• The expression is evaluated once.
• It is compared against case labels.
• The break statement prevents fall-through.
• The default block executes if no match is found.

Arrays in C: 1D and 2D

An Array is a collection of elements of the same data type stored in contiguous memory.

• 1D Array: Represents a single row of linear data (e.g., int arr[5];).
• 2D Array: Represents data in a tabular layout (e.g., int matrix[2][2];).

Functions and Call by Reference

A Function is a reusable block of code. In Call by Reference, pointers are passed to modify original memory values.

Origin and Features of C Language

• Origin: Created by Dennis Ritchie in 1972 at Bell Labs.
• Applications: Operating systems, embedded systems, compilers, and databases.
• Key Features: Procedural, fast, portable, low-level memory access, and extensive standard libraries.