if - legal expressions

The expressions that an if statement evaluates must either be convertible to an int: 
if(1)
     cout << "1 is equivalent to true\n";
or to a char: 
if('f')
     cout << "\'f\' is equivalent to true\n";
or to a floating-point value: 
if(3.5)
     cout << "3.5 is equivalent to true\n";
or to a pointer: 
int *p, a;
a = 4;
p = &a;
if(p)
     cout << "p (the address it contains) is equivalent to true\n";
Any expression evaluating to such values is legal for an if statement, including assignments: 
if(int d = 4 * 7)
     cout << "d\'s value is " << d << endl;
and functions: 
if(by10(5) > 30)
    cout << by10(5) << " is greater than 30\n";
Further, an alternative statement can be executed in case the expression evaluated by the if statement evaluates to false: 
if(a > 0)
     cout << "a is greater than 0\n";
else
     cout << "a is smaller than, or equal to, 0\n";
else precedes the alternative statement. Such a statement can also be another if statement: 
if(b > 0)
     cout << "b is greater than 0\n";
else if(b < 0)
     cout << "b is smaller than 0\n";
else
     cout << "b is equal to 0\n";


Example


#include <iostream>
using namespace std;

int by10(int x)
{
     return x * 10;
}

int main()
{   
     if(1)
           cout << "1 is equivalent to true\n";

     if(3.5)
           cout << "3.5 is equivalent to true\n";

     if('f')
           cout << "\'f\' is equivalent to true\n";

     int *p, a;
     a = 4;
     p = &a;
     if(p)
           cout << "p (the address it contains) is equivalent to true\n";

     if(by10(5) > 30)
           cout << by10(5) << " is greater than 30\n";

     if(int d = 4 * 7)
           cout << "d\'s value is " << d << endl;
     if(a > 0)
           cout << "a is greater than 0\n";
     else
           cout << "a is smaller than, or equal to, 0\n";
     int b = 0;
     if(b > 0)
           cout << "b is greater than 0\n";
     else if(b < 0)
           cout << "b is smaller than 0\n";
     else
           cout << "b is equal to 0\n";
}

Output

3
5
3