Comparing two values

Hello guys! Im kinda newbie here… im making code where i want to compare if key value is in the nt array but i can’t make it…

/* @file MultiKey.ino
|| @version 1.0
|| @author Mark Stanley
|| @contact mstanley@technologist.com
||
|| @description
|| | The latest version, 3.0, of the keypad library supports up to 10
|| | active keys all being pressed at the same time. This sketch is an
|| | example of how you can get multiple key presses from a keypad or
|| | keyboard.
|| #
*/

#include <Keypad.h>
#include <pitches.h>

const byte ROWS = 4; //four rows
const byte COLS = 4; //three columns
char keys[ROWS][COLS] = {
{'1','2','3', 'A'},
{'4','5','6', 'B'},
{'7','8','9', 'C'},
{'*','0','#', 'D'}
};
char notes[]={NOTE_C4, NOTE_D4, NOTE_E4, NOTE_F4, NOTE_G4, NOTE_A4, NOTE_B4, NOTE_C5};
byte rowPins[ROWS] = {9, 8, 7, 6}; //connect to the row pinouts of the kpd
byte colPins[COLS] = {5, 4, 3, 2}; //connect to the column pinouts of the kpd
const char nt[]= {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
int i;
Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );

unsigned long loopCount;
unsigned long startTime;
String msg;


void setup() {
    Serial.begin(9600);
    loopCount = 0;
    startTime = millis();
    msg = "";
}


void loop() {
    loopCount++;
    if ( (millis()-startTime)>5000 ) {
        Serial.print("Average loops per second = ");
        Serial.println(loopCount/5);
        startTime = millis();
        loopCount = 0;
    }

    // Fills kpd.key[ ] array with up-to 10 active keys.
    // Returns true if there are ANY active keys.
    if (kpd.getKeys())
    {
        for (int i=0; i<LIST_MAX; i++)   // Scan the whole key list.
        {
            if ( kpd.key[i].stateChanged )   // Only find keys that have changed state.
            {
                switch (kpd.key[i].kstate) {  // Report active key state : IDLE, PRESSED, HOLD, or RELEASED
                    case PRESSED:
                    msg = " PRESSED.";
                break;
                    case HOLD:
                    msg = " HOLD.";
                break;
                    case RELEASED:
                    msg = " RELEASED.";
                break;
                    case IDLE:
                    msg = " IDLE.";
                }
                Serial.print("Key ");
                Serial.print(kpd.key[i].kchar);
                Serial.println(msg);
                
            }
        }
    }
    if(msg == " HOLD." || msg == " PRESSED." ){
       char kyprs = kpd.key[i].kchar;
      if(strcmp(kyprs, nt)!= 0) // Here i want to compare them...
{
        i= kpd.key[i].kchar;
      tone(10, notes[i]);
      }
    }
    else{
      noTone(10);
    }
}  // End loop

Hello and welcome,

You could do that without an array:

if ( kyprs >= '0' && kyprs <= '9' )

Since these are single chars, not strings, you can just use == and skip strcmp().