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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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write a program to implement atoi function in c

Description:

    • int my_atoi(const char *s)
      • The function will recieve a string and covert the number stored in the string into exact integer number.
      • Return the number.
Pr-requisites:-
    • Functions
    • Pointers

Objective: -

  • To understand the concept of
    • Functions and Pointers
Inputs: -
          String, String and Integer

Sample execution: -
Test Case 1 :
Enter a numeric string: 12345
String to integer is 12345

Test Case 2 :
Enter a numeric string: -12345
String to integer is -12345

Test Case 3 :
Enter a numeric string: +12345
String to integer is 12345

Test Case 4 :
Enter a numeric string: +-12345
String to integer is 0

Test Case 5 :
Enter a numeric string: 12345-
String to integer is 12345

Test Case 6 :
Enter a numeric string: abcd12345
String to integer is 0

Test Case 7 :
Enter a numeric string: 12345abcd

String to integer is 12345


PROGRAM

----------------------------------------------------------------------------------------------------------------------------


#include <stdio.h>

int my_atoi(const char str[])

{

    int i=0,a=0,b=0,t=0;

    while(str[i]!='\0')

    {

        if(str[0]=='*')

        {

            break;

        }

        if((str[0]=='-' && str[1]=='+') || (str[0]=='+' && str[1]=='-') || (str[0]=='+' && str[1]=='+') || (str[0]=='-' && str[1]=='-'))

        {

            break;

        }

        if((str[i]>='a' && str[i]<='z') || (str[i]>='A' && str[i]<='Z'))

        {

            break;

        }

        if(str[0]=='-')

        {

            t=1;

         //   i++;

        }

        if(str[i]>='0' && str[i]<='9')

        {

            b=str[i]-48;

            a=a*10+b;

            

        }

        i++;

    }

    if(t==1)

    return -a;

    else

    return a;

}

int main()

{

    char str[20];

      printf("Enter a numeric string : ");

    scanf("%s", str);

    int res = my_atoi(str);

    printf("String to integer is %d\n", res);

}

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