if statement - C++ Logicial Operators ( Could someone Explain and help) -

so have written small program work out perimeter of simple shapes (very new coding keeping simple). stuck though code works triangle , can't life of me work out how last logical operator work!!!? appreciate time , advice best regards jake

#include <iostream> #include <string> using namespace std; int main () {        int length;     int diameter;     float pi = 3.14;     string shape;     string square = "square";     string triangle = "triangle";     string circle = "circle";                cout <<"=======================" << endl;     cout <<"=welcome perimeters=" << endl;     cout <<"#######################" << endl;     cout <<"###|select shape|####" << endl;      cout <<"=======================" << endl;     cout <<"=   |   circle   |    =" << endl;     cout <<"=   |  triangle  |    =" << endl;        cout <<"=   |   square   |    =" << endl;     cout <<"=======================" << endl;       cout <<"enter shape >; ";     cin >> shape;      if (shape == "square") {         cout << "enter length of side >: ";         cin >> length;         cout <<  "perimeter = " ;          cout << length * 4 <<endl;     } else {              (shape == "triangle"){               cout << "enter length of side >: ";              cin >> length;              cout <<  "perimeter = " ;               cout << length * 3 <<endl;              }                  }                else  {                     (shape == "circle") {                      cout << "enter diameter >: ";                     cin >> diameter;                     cout <<  "perimeter = " ;                      cout << diameter * pi <<endl;                     }                     }         return 0; } 

you not writing else-if statement correctly. should in form:

if(boolean expression) {} else if (boolean expression) {} // many else ifs need else {} // optional 

therefore else if conditionals should be:

if (shape == "square") {     cout << "enter length of side >: ";     cin >> length;     cout <<  "perimeter = " ;      cout << length * 4 <<endl; } else if (shape == "triangle"){     // , on... } else {     cout << "invalid shape entered."; } 

additionally, pi isn't 3.14. include <math.h> , use m_pi.