for loop

 iteration\_expression   -   any [expression](expressions), which is executed after every iteration of the loop and before re-evaluating condition. Typically, this is the expression that increments the loop counter     statement   -   any [statement](statements), typically a compound statement, which is the body of the loop   

for (;;)
    int n;
// n goes out of scope

for (int i = 0; ; ) {
    long i = 1;   // valid C, invalid C++
    // ...
}

#include <iostream>
#include <vector>
 
int main()
{
    // typical loop with a single statement as the body
    for (int i = 0; i < 10; ++i)
        std::cout << i << ' ';
    std::cout << '\n';
 
    // init-statement can declare multiple names, as long as they
    // can use the same decl-specifier-seq
    for (int i = 0, *p = &i; i < 9; i += 2) {
        std::cout << i << ':' << *p << ' ';
    }
    std::cout << '\n';
 
    // condition may be a declaration
    char cstr[] = "Hello";
    for (int n = 0; char c = cstr[n]; ++n)
        std::cout << c;
    std::cout << '\n';
 
    // init-statement can use the auto type specifier
    std::vector<int> v = {3, 1, 4, 1, 5, 9};
    for (auto iter = v.begin(); iter != v.end(); ++iter) {
        std::cout << *iter << ' ';
    }
    std::cout << '\n';
 
   // init-statement can be an expression
    int n = 0;
    for (std::cout << "Loop start\n";
         std::cout << "Loop test\n";
         std::cout << "Iteration " << ++n << '\n')
        if(n > 1)
            break;
    std::cout << '\n';
}

0 1 2 3 4 5 6 7 8 9 
0:0 2:2 4:4 6:6 8:8 
Hello
3 1 4 1 5 9 
Loop start
Loop test
Iteration 1
Loop test
Iteration 2
Loop test

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