Changing case of alphabets

#include<iostream>
using namespace std;
int main()
{
char line[100],c;
cout<<"Enter a string:"<<endl;
cin.getline(line,100);
cout<<"\nThe entered string is...\n";
cout<<line;
    cout<<"\n\n";
    cout<<"The string after conversion...\n\n";
for(int i=0;line[i]!='\0';i++)
{
if(line[i]>=65 && line[i]<=90)
{
line[i]=line[i]+32;
}
else if(line[i]>=97 && line[i]<=122)
{
line[i]=line[i]-32;
}
cout<<line[i];
}
  return 0;
}