for – function in section

Each of the for sections can be filled with any type of expression, including a function’s result. The middle section needs to be either a conditional expression or an expression which can be converted into a bool. The following loop, for example, is perfectly legal and will iterate until it is broken out of. 
for(10; 10; 10)
{// body}
In the next loop each section is filled with a function call. The loop will iterate until it is broken out of, since the function returns 1. 
int f()
{
     return 1;
}

for(f(); f(); f())
{// body}
Notice that the first and third section of a for loop can be filled with a function returning any type of result, even a void: 
void g()
{}

for(g(); f(); g())
{// body}
The middle section, though, cannot contain a void (the value must be convertible into a bool).

Example


#include <iostream>
#include <ctime>
using namespace std;
 
int f()
{
     return 1;
}

void g()
{}

float h()
{
     return 1.1f;
}

int main()
{   
     int i = 0;

     for(10; 10; 10)
     {
          cout << "Loop 1 - Enter a number: ";
           cin >> i;
           if(i == 0)
                break;
     }

     cout << endl;

     for(f(); f(); f())
     {
           cout << "Loop 2 - Enter a number: ";
           cin >> i;
           if(i == 0)
                break;
     }

     cout << endl;

     for(g(); f(); g())
     {
           cout << "Loop 3 - Enter a number: ";
           cin >> i;
           if(i == 0)
                break;
     }

     cout << endl;

     for(h(); h(); h())
     {
           cout << "Loop 4 - Enter a number: ";
           cin >> i;
           if(i == 0)
                break;
     }
}

Output

Loop 1 - Enter a number: 3
Loop 1 - Enter a number: 0

Loop 2 - Enter a number: 5
Loop 2 - Enter a number: 0

Loop 3 - Enter a number: 1
Loop 3 - Enter a number: 0

Loop 4 - Enter a number: 6
Loop 4 - Enter a number: 0