how to make my program unable to mix letters and numbers

i need a help to fix this. so, i have program like this.

main{ char name[15];  while(cout<<"Name : " && !(cin.getline(name, 15)) || !isalpha(nomor[0])){             cout<<"\nPlease enter data correctly!\n";             cin.clear();             cin.ignore(numeric_limits<streamsize>::max(), '\n');  } } 

when the program running, program can’t enter number like this Name : 2 but if i input like this, Name : michel12312321321 program the program will still process the next statement