#include <iostream>

int main()
{
  int number = 175718;
  int result = 0;

  while(number){
    int digit = number % 10;
    
    switch(digit)
    {
      case 1:
      break;
      
      case 7:
        result *= 10;
        result += 8 ;
      break;

      default:
        result *= 10;
        result += digit;
      break;
    }

    number /= 10;
  }

  std::cout << "Result: " << result << std::endl; 

  return 0;     
}

Result: 8858