55 lines
964 B
C++
55 lines
964 B
C++
/*
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Nome: Mario
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Cognome: Montanari
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Classe: 3AIN
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Data: 11/03/2025
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*/
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#include <iostream>
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#include <cctype>
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#define SIZE 100+1
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using namespace std;
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char *decryptAffineCipher(char *const str, const int a, const int b);
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int main(void) {
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char str[SIZE];
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int a;
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int b;
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cout << "Inserisci una frase: ";
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cin.getline(str, SIZE);
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cout << "a: ";
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cin >> a;
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cout << "b: ";
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cin >> b;
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cout << "Frase codificata: " << decryptAffineCipher(str, a, b) << endl;
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return 0;
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}
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char *decryptAffineCipher(char *const str, const int a, const int b) {
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int a_inv = 0;
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for (int i = 0; i < 26; i++) {
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if ((a * i) % 26 == 1) {
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a_inv = i;
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break;
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}
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}
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for (int i = 0; str[i] != '\0'; i++) {
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if (isupper(str[i])) {
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str[i] = ((a_inv * ((str[i] - 'A') - b + 26)) % 26) + 'A';
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} else if (islower(str[i])) {
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str[i] = ((a_inv * ((str[i] - 'a') - b + 26)) % 26) + 'a';
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}
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}
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return str;
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} |