Use of strncmp function in C

strncmp() function

The strncmp function in C is used to compare a specified number of characters from the beginning of two strings. It is defined in the <string.h> header file.

Purpose:

• Partial String Comparison: strncmp is useful when only a portion of a string needs to be compared, rather than the entire string. This is particularly relevant when dealing with prefixes, command parsing, or verifying specific patterns at the start of a string.
• Bounded Comparison: It provides a safeguard against buffer overflows by limiting the number of characters compared.

How it works:
The function takes three arguments: two pointers to the strings to be compared (str1 and str2), and an integer n representing the maximum number of characters to compare. It compares characters lexicographically, one by one, from the beginning of each string until "mismatch is found".

Function Syntax

• int strncmp(const char *str1, const char *str2, size_t n);

Parameters:

• str1 → first string
• str2 → second string
• n → number of characters to compare

Return Value of function:

• Zero (0): If the first n characters of both strings are equal.
• Positive value: if first differing character in str1 is greater than that in str2 (difference ASCII value)
• Negative value: if first differing character in str1 is less than that in str2 (difference of ASCII value)

Example

#include <stdio.h>

#include <string.h>

int main() {

    char str1[] = "Computer";

    char str2[] = "Compute";

   

    // Compare first 7 characters

    int result = strncmp(str1, str2, 7);

    if (result == 0)

        printf("First 7 characters are same.\n");

    else if (result > 0)

        printf("str1 is greater than str2.\n");

    else

        printf("str1 is smaller than str2.\n");

    return 0;

}

Output of program:

First 7 characters are same.

Use of strstr in C

strstr in C

strstr is a function in C that is used to find the first occurrence of a substring in a string. It is declared in the <string.h> header.

Syntax:

char *strstr(const char *str1, const char *str2);

• str1 → The main string in which you want to search.
• str2→ The substring you are searching for.

Returns:

• A pointer to the first occurrence of str2 in str1.
• NULL if str2 is not found.

Example:

#include <stdio.h>

#include <string.h>

int main() {

    char str[] = "Hello, welcome to C programming!";

    char substr[] = "welcome";

    // Using strstr to find substring

    char *result = strstr(str, substr);

    if (result != NULL) {

        printf("Substring found at position: %ld\n", result - str);

    } else {

        printf("Substring not found.\n");

    }

    return 0;

}

Output:

Substring found at position: 7

Viva questions based on C Decision Making statements with Answers

Viva Questions on C Decision Making Statements with Answers

(if, if-else, nested if, switch, conditional operator)

1. What is a decision-making statement in C?

Answer:

A decision-making statement allows the program to take different actions based on conditions. Examples are if, if-else, nested if, switch, and the conditional (ternary) operator ?:.

2. What is the difference between if and if-else statements?

Answer:

if executes a block of code only if the condition is true.
if-else provides an alternative block of code to execute when the condition is false.

3. Can we use multiple if-else statements in C?

Answer:

Yes, we can use multiple if-else if constructs, also known as ladder if-else, to check multiple conditions sequentially.

4. What is a nested if statement?

Answer:

A nested if means writing an if statement inside another if or else block. It is useful when multiple levels of decision-making are required.

5. How does a switch statement work in C?

Answer:

A switch evaluates an expression and compares it with multiple case labels. When a match is found, the corresponding block is executed until a break statement is encountered.

6. What happens if we don’t use break in a switch case?

Answer:

Without break, the program executes the matched case and then continues executing subsequent cases (fall-through) until it encounters a break or the end of the switch block.

7. Can a switch statement work with floating-point values?

Answer:

No, in C, a switch statement works only with integer and character values, not with float or double.

8. What is the difference between if-else and switch?

Answer:

if-else can handle complex conditions (logical expressions, ranges, multiple conditions).
switch is limited to checking equality of a single expression against constant values but is often faster and more readable.

9. What is the conditional (ternary) operator in C?

Answer:

The conditional operator ?: is a shorthand for if-else.

Example:

int max = (a > b) ? a : b;

This assigns a to max if a > b, otherwise assigns b.

10. Is it possible to use a switch inside another switch?

Answer:

Yes, we can have nested switch statements, but it is not commonly used because it reduces readability.

11. What is the difference between = and == in decision-making?

Answer:

= is the assignment operator (assigns value).
== is the equality operator (compares two values).
Using = instead of == inside conditions is a common error.

12. Can if statements be written without curly braces {}?

Answer:

Yes, if there is only one statement inside the if or else block, curly braces are optional. But for multiple statements, curly braces are required.

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C Programming Viva Questions on Loops with Model Answers

Viva Questions on Loops with Answers

1. What is a loop in C programming? Why do we use it?

Answer:

A loop is a control structure in C that repeatedly executes a block of code until a specified condition is true. We use loops to avoid writing repetitive code and to perform iterative tasks efficiently.

2. Explain the difference between while, do…while, and for loops in C.

Answer:

• while loop: Condition is checked first, then the body executes. (Entry-controlled loop)
• do…while loop: Body executes first, then condition is checked. (Exit-controlled loop, runs at least once)
• for loop: Used when initialization, condition, and increment/decrement are all in one line. Best for fixed iterations.

3. What happens if the loop condition is never satisfied in a while loop?

Answer:

If the condition is false at the beginning, the while loop body will never execute even once.

4. Can a for loop run infinitely? Give an example.

Answer:

Yes. If the loop condition is always true or missing, the loop runs infinitely.

Example:

for(;;) {

   printf("Infinite loop\n");

}

5. What is the difference between break and continue statements inside loops?

Answer:

•   break: Immediately exits the loop and transfers control outside.

•   continue: Skips the current iteration and jumps to the next iteration of the loop.

6. What is an infinite loop? Write a simple example in C.

Answer:

An infinite loop is a loop that never terminates because the condition always remains true.

Example:

while(1) {

   printf("Hello\n");

}

7. How is the initialization, condition, and increment part of a for loop optional? Give an example.

Answer:

All three parts in a for loop are optional. If omitted, they must be handled inside the loop body.

Example:

int i = 1;

for(; ; ) {

   if(i > 5) break;

   printf("%d ", i);

   i++;

}

8. What is the output of the following code?

int i = 1;

while(i <= 5){

    printf("%d ", i);

    i++;

}

Answer:

Output:

1 2 3 4 5

9. Write a C program to print numbers from 1 to 10 using a do…while loop.

Answer:

#include <stdio.h>

int main() {

    int i = 1;

    do {

        printf("%d ", i);

        i++;

    } while(i <= 10);

    return 0;

}

10. Explain nested loops with an example (e.g., printing a multiplication table).

Answer:

A nested loop is a loop inside another loop.

  

Example of Multiplication table:

for(int i = 1; i <= 3; i++) {

    for(int j = 1; j <= 3; j++) {

        printf("%d ", i * j);

    }

    printf("\n");

}

Output:

1 2 3  

2 4 6  

3 6 9

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C Programming Viva Questions Data Types

Viva Questions based on C Programming Data Types

 

1. What are data types in C?

Answer: It defines the type of data that we can store in a variable. They tell the compiler how much space to allocate and how to interpret the value.

 

2. What are the different types of data types in C?

Answer: C has three primary data types:

•   Basic data types: int, float, char, double

•   Derived data types: array, pointer, structure, union

•   Enumeration and void types: enum, void

 

3. What is the size of int, float, double, and char in C?

Answer: Sizes may vary by system, but typically:

•   int: 4 bytes

•   float: 4 bytes

•   double: 8 bytes

•   char: 1 byte

 

4. What is the difference between float and double?

Answer:

•   float is a single-precision (32-bit) floating point.

•   double is a double-precision (64-bit) floating point. double is more accurate and can store larger values.

 

5. What is the use of the void data type?

Answer: void means “no type.” It is used:

•   In functions that return nothing: void functionName()

•   For generic pointers: void *ptr

 

6. What is the difference between signed and unsigned data types?

Answer:

•   Signed data types can store both positive and negative values.

•   Unsigned data types can only store positive values, which allows a larger positive range.

Example:

signed int ranges from –2,147,483,648 to 2,147,483,647

unsigned int ranges from 0 to 4,294,967,295

 

7. What is the use of sizeof operator?

Answer: The sizeof operator returns the size (in bytes) of a data type or variable.

Example: sizeof(int) gives 4 on most systems.

 

8. What are type modifiers in C?

Answer: Type modifiers are keywords that alter the meaning of the base data types.

They are: signed, unsigned, long, and short.

Example: unsigned long int increases the range for positive integers.

 

9. Can we use char for storing small integers?

Answer: Yes. A char is 1 byte, so it can store small integer values (typically –128 to 127 for signed char).

 

10. What happens if we assign a float value to an int variable?

Answer: The decimal part is truncated, not rounded.

Example:

float x = 5.9;

int y = x; // y becomes 5

 

 

Important Computer Network Terminology

Hello Reader,

If you have an interest in network programming, it's essential to familiarize yourself with the following key terminology associated with computer networks.  

Basic Networking Terms

1. IP Address: A unique identifier assigned to a device on a network.
2. Subnet Mask: Defines the network and host portions of an IP address.
3. MAC Address: A unique identifier assigned to a device's network interface card (NIC).
4. Gateway: A device that connects different networks and facilitates communication.
5. DNS (Domain Name System): Translates domain names to IP addresses.
6. DHCP (Dynamic Host Configuration Protocol): Assigns IP addresses automatically to devices on a network.
7. LAN (Local Area Network): A network that spans a small geographical area.
8. WAN (Wide Area Network): A network that spans a large geographical area.
9. VPN (Virtual Private Network): Creates a secure connection over a public network.
10. SSID (Service Set Identifier): The name of a wireless network.

Protocols

1. TCP (Transmission Control Protocol): Ensures reliable data transmission.
2. UDP (User Datagram Protocol): A connectionless protocol for faster, less reliable data transmission.
3. HTTP (Hypertext Transfer Protocol): Used for transferring web pages.
4. HTTPS (HTTP Secure): A secure version of HTTP.
5. FTP (File Transfer Protocol): For transferring files over a network.
6. SMTP (Simple Mail Transfer Protocol): Used for sending emails.
7. IMAP (Internet Message Access Protocol): Accesses emails on a server.
8. SNMP (Simple Network Management Protocol): Manages network devices.
9. ICMP (Internet Control Message Protocol): Used for error reporting and diagnostics (e.g., ping).
10. ARP (Address Resolution Protocol): Maps IP addresses to MAC addresses.

Network Devices

1. Router: Directs data packets between networks.
2. Switch: Connects devices within a LAN.
3. Hub: A basic device to connect multiple devices in a network.
4. Modem: Connects a network to the internet.
5. Firewall: Monitors and controls incoming and outgoing network traffic.
6. Access Point (AP): Provides wireless connectivity in a network.
7. Bridge: Connects two LANs.

Security Terms

1. Firewall: A device or software to block unauthorized access.
2. Proxy: Acts as an intermediary between clients and servers.
3. Encryption: Secures data by converting it into an unreadable format.
4. Authentication: Verifies the identity of a user or device.
5. VPN Tunnel: An encrypted connection within a VPN.
6. Intrusion Detection System (IDS): Detects unauthorized access attempts.
7. Intrusion Prevention System (IPS): Prevents unauthorized access.

Network Types

1. MAN (Metropolitan Area Network): Covers a city or a large campus.
2. SAN (Storage Area Network): Dedicated for data storage.
3. PAN (Personal Area Network): Covers personal devices (e.g., Bluetooth).
4. CAN (Campus Area Network): Covers a campus or organization.
5. IoT (Internet of Things): A network of interconnected smart devices.

Advanced Concepts

1. NAT (Network Address Translation): Maps private IPs to public IPs.
2. QoS (Quality of Service): Prioritizes network traffic.
3. BGP (Border Gateway Protocol): Manages routing between autonomous systems.
4. MPLS (Multiprotocol Label Switching): Directs data using labels for efficient routing.
5. Load Balancer: Distributes network traffic across multiple servers.
6. VLAN (Virtual LAN): Segments a network into logical parts.
7. Cloud Networking: Using cloud-based infrastructure for networking.

Measurement and Monitoring

1. Bandwidth: Maximum data transfer capacity of a network.
2. Latency: Time delay in data transmission.
3. Throughput: Actual data transfer rate.
4. Packet: A small unit of data transmitted over a network.
5. Ping: Tests network connectivity and measures latency.
6. Traceroute: Tracks the path data takes to reach its destination.

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