i want to do program that calculat percentage of error

percentage of error ={ X ( calculated) * X ( measuered) } * 100 / { X ( measuered)}

and if the result more than or equal 50 it is bad

if it is less than 50 til 20 it is good

if it is less than 20 it is excelente

the programe must have ( if , case , while , switch, functions)

i relly need help

all what i know

i will write it down

so i wish to help me

# include < iostream>

using namespace std;

int main ( void)

int main (math.h)

for(i==50

cout <<" enter your x calculated"<<\n;

cin>> x calculated

cout <<" enter x measured"<<\n;

cin>> X measured;

if(x==>50);

cout<< "bad result"<<;

if else( x=<50, x==>20);

cout<<" good result";

else( x=<20)

cout<<" excellent result"<<;