Loops

In programming, loops are used to repeat a block of code multiple times. They’re like a set of instructions that the computer repeats until a certain condition is met.

While Loops:

A while loop repeatedly executes as long as a specified condition is true. It’s like saying “Keep doing this while something the condition is met”. While loops are useful when the number of times needed to repeat the instructions is unknown.

while (condition) {
	// execute block
}

Code Example:

Here’s an example of a while loop that reads user input and outputs the value:

int input;
while (cin >> input) {
  cout << input << '\n';
}

To stop inputting values hit ctrl-d to end the loop. When ctrl-d is pressed the condition for the while loop is no longer true.

For Loops:

A for loop is used to iterate (or loop) over a range of values. It’s like saying “Do this for a specific number of times”. For loops are useful while the number of iterations is already known.

for (initialization; condition; increment/decrement) {
	// execute block
}

The syntax for a for loop is not as straightforward, but after seeing it a few times, you’ll quickly see the pattern.

With a typical for loop, we do the following:

1. Define a variable (usually an integer) to keep track of the current iteration inside the loop.
2. Define a stopping condition.
3. Increment the loop.

Code Example:

Here’s an example of a for loop that will be executed 5 times where i is the value of the current index or iteration of the loop:

for (int i = 0; i < 5; i++) {
  cout << i;
}
cout << '\n';

This loop will print out 01234.

Ranged-Based For Loop:

The last thing I should cover is a range-based for loop. Ranged-based loops are similar to foreach loops in other languages. For example, “for each” char in a string do something!

In this snippet, the ranged-based loop capitalized each letter in the given string.

string str = "hello!";
for (char c : str) {
  if (c >= 'a' && c <= 'z') {
    c += ('A'-'a');
  }
}
cout << str << '\n';  // HELLO!

The Difference:

While Loop: Used when you want to repeat a block of code based on a condition. You might not know in advance how many times the loop will run.

For Loop: Used when you know exactly how many times you want to repeat a block of code. It’s great for iterating over a range of values or performing a specific task a known number of times. For example, looping over arrays or strings!

Depending on your specific use case, you can reproduce the same results with either loop.