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#include <iostream>
#include <cmath>
using namespace std;
 
double x1, y1, x2, y2;
 
int main()
{
    cout << "Input x1, y1: ";
    cin >> x1, y1;
    cout << "Input x2, y2: ";
    cin >> x2, y2;
 
    cout << "Distance between points: " << sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
 
    return 0;
}
 

prog.cpp:5:12: error: ‘double y1’ redeclared as different kind of symbol
 double x1, y1, x2, y2;
            ^
In file included from /usr/include/features.h:371:0,
                 from /usr/include/i386-linux-gnu/c++/4.8/bits/os_defines.h:39,
                 from /usr/include/i386-linux-gnu/c++/4.8/bits/c++config.h:426,
                 from /usr/include/c++/4.8/iostream:38,
                 from prog.cpp:1:
/usr/include/i386-linux-gnu/bits/mathcalls.h:242:1: error: previous declaration of ‘double y1(double)’
 __MATHCALL (y1,, (_Mdouble_));
 ^
prog.cpp: In function ‘int main()’:
prog.cpp:10:18: warning: right operand of comma operator is a reference, not call, to function ‘y1’ [-Waddress]
     cin >> x1, y1;
                  ^
prog.cpp:10:18: warning: right operand of comma operator has no effect [-Wunused-value]
prog.cpp:12:18: warning: right operand of comma operator has no effect [-Wunused-value]
     cin >> x2, y2;
                  ^
prog.cpp:14:76: error: invalid operands of types ‘double’ and ‘double(double)throw ()’ to binary ‘operator-’
     cout << "Distance between points: " << sqrt(pow(x2 - x1, 2) + pow(y2 - y1, 2));
                                                                            ^

Standard output is empty