for loop iterations in C++, Javascript, Python

for loop cheat sheet

C++

Range-based for loop over iterable

for ( range_declaration : range_expression ) 
    loop_statement
// Iterating over whole array 
std::vector<int> v = {0, 1, 2, 3, 4, 5}; 
for (auto i : v) 
    std::cout << i << ' ';
// the initializer may be a braced-init-list
for (int n : {0, 1, 2, 3, 4, 5})
    std::cout << n << ' '
// Printing string characters
std::string str = "Poby";
for (char c : str)
    std::cout << c << ' ';
// Printing keys and values of a map
std::map <int, int> MAP({{1, 1}, {2, 2}, {3, 3}});
for (auto i : MAP)
    std::cout << '{' << i.first << ", " << i.second << "}\n";

for_each
Applying a function to a range

void myfunction (int i) {  // function:
  std::cout << ' ' << i;
}
std::vector<int> v = {0, 1, 2, 3, 4, 5};
for_each (v.begin(), v.end(), myfunction);

Javascript

• for statement
• for … in statement
• for … of statement

for statement

for (let step = 0; step < 5; step++) {
  // Runs 5 times, with values of step 0 through 4.
  console.log('Walking east one step');
}

for … in statement

iterate over property names

const arr = [3, 5, 7];
arr.foo = 'hello';
for (let i in arr) {
   console.log(i); // logs "0", "1", "2", "foo"
}

for … of statement

iterate over property values

const arr = [3, 5, 7];
arr.foo = 'hello';
for (let i of arr) {
   console.log(i); // logs 3, 5, 7
}

Iterate through a Map

ES6

var myMap = new Map();
myMap.set("0", "foo");
myMap.set(1, "bar");
myMap.set({}, "baz");

for (const [key, value] of myMap.entries()) {
  console.log(key, value);
}
// 0 foo
// 1 bar
// {} baz

ES8

const object = {'a': 1, 'b': 2, 'c' : 3};
for (const [key, value] of Object.entries(object)) {
  console.log(key, value);
}
// a 1
// b 2
// c 3

Python

loop over range

for x in range(0, 3):
    print("We're
 on time %d" % (x))

loop over iterable

string as an iterable

string = "Hello World"
for x in string:
    print(x)

list as an iterable

collection = ['hey', 5, 'd']
for x in collection:
    print(x)

loop over dictionary

print all keys

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
for x in thisdict:
  print(x)
// result
brand
model
year

print all values

for x in thisdict:
  print(thisdict[x])
// result
Ford
Mustang
1964

loop over value
use “values()”

for x in thisdict.values():
  print(x)
// result
Ford
Mustang
1964

loop over both keys and values

for x, y in thisdict.items():
  print(x, y)
// result
brand Ford
model Mustang
year 1964