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C Program to Check Prime Number Using Efficient Logic

  Introduction A prime number is a number that has exactly two distinct positive divisors: 1 and itself. In this program, we check whether a given number is prime or not using a simple and efficient logic. This type of program is commonly used in mathematics, competitive programming, and basic algorithm learning for beginners in C programming. Problem Statement The task is to write a C program that determines whether a given integer is a prime number or not. The program takes a single integer input from the user and analyzes its divisibility. If the number has no divisors other than 1 and itself, it should be identified as a prime number; otherwise, it is not prime. This problem is important in number theory and has practical relevance in areas such as cryptography, data validation, and algorithm design.  Algorithm / Logic Explanation To check whether a number is prime, we need to verify that it is not divisible by any number other than 1 and itself. The algorithm follows a si...
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Reverse a String in C

Reverse String in C

Reverse a String in C

This C program reverses a given string using a simple two-pointer technique. It swaps characters from both ends until the middle is reached.

✅ C Program Code:


#include <stdio.h>
#include <string.h>

void reverse(char str[])
{
    int start = 0;
    int end = strlen(str) - 1;
    int temp;
    while (start < end)
    {
        temp = str[start];
        str[start] = str[end];
        str[end] = temp;
        start++;
        end--;
    }
}

int main()
{
    char str[100];
    printf("Enter the string:\n");
    scanf("%[^\n]", str);
    printf("Before reversing the string: %s\n", str);
    reverse(str);
    printf("After reversing the string: %s", str);
}

📌 How It Works:

  • reverse(): Swaps characters from start and end using a while loop until the full string is reversed.
  • scanf("%[^\n]", str): Reads a line of input including spaces.
  • main(): Takes user input, prints original and reversed string.

💻 Sample Output:

Enter the string:
Hello World
Before reversing the string: Hello World
After reversing the string: dlroW olleH

🔍 Keywords:

reverse string in C, string handling in C, two-pointer approach C, beginner string program, C logic examples, character array reverse

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