how to round off to one decimal in c++ code example

Example 1: round double to n decimal places c++

float roundoff(float value, unsigned char prec)
{
  float pow_10 = pow(10.0f, (float)prec);
  return round(value * pow_10) / pow_10;
}

auto rounded = roundoff(100.123456, 3);
// rounded = 100.123;

Example 2: get number round off to two decimal places c++

float a,b,c,d,sum;

 cin>>a>>b>>c>>d; // reading decimal values

sum=(a*b*c*d);

sum=round(sum*100)/100; // here it is for 2 decimal points

if((float)sum < (float) 9.58)
  cout<<"YES\n";
else
  cout<<"NO\n";