Find the sum of the ASCII values ​​of characters in prime positions

introduce

In this tutorial, we will learn the concept of C to find the sum of ASCII values ​​of characters appearing in primary positions. Prime positions are characters with positions 2, 3, 5, or any other prime number.

ASCII (American Standard Code for Information Interchange) values ​​are unique numerical values ​​for letters, letters, punctuation marks, and other characters used in encoding. It is used to communicate with computers because computers cannot understand human language.

There are 128 ASCII values, from 0 to 127. Uppercase and lowercase letters have different ASCII values.

We will develop a C code to calculate the ASCII value of a character located in a prime position. We use the length() function of the string class to store the length of the input string.

Example 1

There is an string = “Hello”
Sum of prime position ASCII value characters = 320

In the above string “Hello” the ASCII value of each character is 
H =  72
e = 101
l = 108
l = 108
o = 111

The characters in the prime position are "e", "l", and "o". Add the ASCII values ​​of the characters in these prime positions.

Sample 2

Input string = “abcd”
Sum = 197

The main position characters in the input string "abcd" are "b" and "c".

The ASCII value of input string characters is as listed:
a = 97
b = 98
c = 99
d = 100

Calculate the sum of the ASCII values ​​of the characters at the primary position in the string.

grammar

• sqrt() − This library function is defined in the math library and it returns the square root of the input number

sqrt(n)

• length() − This string library function returns the length of the input string, where the length is the number of characters in the string.

string_name.length(); 

Example 1

We will use the C programming language to implement an example that calculates the sum of the ASCII values ​​of characters located at prime positions in the input string. The C code input string is "Hello". We first find all prime positions of the input string by applying the logic of identifying prime numbers. Use a for loop to find the ASCII values ​​of all characters of the input string. Sums the ASCII values ​​of input string characters at prime positions.

#include <iostream>
#include <string>
#include <vector>

using namespace std;

// User-defined function to find the prime positions 
bool find_prime(int p){
   if (p <= 1) {
      return false;
   }
   // loop to check the prime number
   for (int x = 2; x*x <= p; x++) {
      if (p % x == 0) {
         return false;
      }
   }
   return true;
}

// user-defined function to sum ASCII values of the prime position characters 
int sum_of_primes(string st) {
   int sum1 = 0;
   
   //variable to store the input string length.
   int p = st.length();
   vector<bool> primes(p+1, false);
   primes[2] = true;
   for (int x = 3; x <= p; x += 2) {
      primes[x] = find_prime(x);
   }
   for (int x = 2; x <= p; x++){
      if (primes[x] && x <= p){
         sum1 += int(st[x-1]);
      }
   }
   return sum1;
}

// controlling code
int main(){
   string st = "Hello";
   int sum1 = sum_of_primes(st);
   cout << "Sum of ASCII values of characters at prime positions: " << sum1 << endl;
   return 0;
}

Output

"Sum of ASCII values of characters at prime positions: 320

Example 2

is translated as:

Example 2

Here, we use different logic to implement this example. We first find the prime position, find these ASCII values ​​in the main() function and add them.

#include <iostream>
#include <cmath>
using namespace std;

bool isNumPrime(int n) {
   if (n < 2)
      return false;
   for (int x = 2; x <= sqrt(n); ++x) {
      if (n % x == 0)
         return false;
   }
   return true;
}

int main() {
   string str = "tutorialspoint";
   //std::cout << "Enter a string: ";
    
   int s = 0;
   for (size_t x = 0; x < str.length(); ++x) {
      if (isNumPrime(x + 1)) {
         s += static_cast<int>(str[x]);
      }
   }
   cout << "Sum of ASCII values at prime positions: " << s << endl;
   return 0;
}

Output

Sum of ASCII values at prime position: 665

in conclusion

In this tutorial, we developed C code to find the sum of the ASCII values ​​of characters at prime positions. We used the length() function of the String class to find the length of the parameter string. ASCII values ​​are predetermined values ​​of letters and other characters used to help computers communicate. In this tutorial, we implemented two examples with different logic and used some C library functions. The most important library function is length(). The length() library function returns the length of a string.

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