cin >> red_rgb;

How to check the red_rgb, green_rgb, blue_rgb variable when entering it, so that only values in the range from 0 to 255 are allowed, while only integers {0,1,2...254,255} are counted, otherwise, you will need to enter the correct value.

int red_rgb = 0;
int green_rgb = 0;
int blue_rgb = 0;    

std::cout << "Enter R: ";
        while (!(cin >> red_rgb) || !(red_rgb >= 0 && red_rgb <= 255))
        {
            cout << "Error";
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
        }
        std::cout << "Enter G: ";
        while (!(cin >> green_rgb) || !(green_rgb >= 0 && green_rgb <= 255))
        {
            cout << "Error";
            cin.clear(); 
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
            
        }
        std::cout << "Enter B: ";
        while (!(cin >> blue_rgb) || !(blue_rgb >= 0 && blue_rgb <= 255))
        {
            cout << "Error";
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
        }

This method tests for a range, but skips semicolons. And if you enter letters instead of numbers, the more letters there are, the more times the cycle will start.

if you enter a float, the cycle for entering the next value is skipped enter image description here

CodePudding user response：

Try something like that:

int inprgb(const string& hint){
    int a=-1;
    while (true){
      cout << hint;
      cin>>a;
      if (cin.fail() || cin.peek()!=10 ||!(a >= 0 && a <= 255) ) {
          cin.clear();
          cout << "Error\n";
          cin.ignore(numeric_limits<streamsize>::max(), '\n');
          continue;
      }
      break;
    }
    return  a;
};

and

red_rgb = inprgb("Enter R: ");