# Solidity – Loops

In Solidity, loops are used to repeat a block of code a certain number of times. Solidity supports different types of loops:

1. For Loop: The for loop is used to execute a block of code a specified number of times. The basic syntax for a for loop is:
``````for (initialization; condition; increment) {
// code to be executed
}
``````

Here’s an example of using a for loop in Solidity:

``````pragma solidity ^0.8.0;
contract Example {
function forLoop() public {
for (uint i = 0; i < 10; i++) {
// code to be executed
}
}
}
``````

In this example, the for loop will execute the code inside the loop 10 times, starting from i = 0, and incrementing by 1 each time.

1. While Loop: The while loop is used to execute a block of code repeatedly as long as a given condition is true. The basic syntax for a while loop is:
``````while (condition) {
// code to be executed
}
``````

Here’s an example of using a while loop in Solidity:

``````pragma solidity ^0.8.0;
contract Example {
uint a = 0;
function whileLoop() public {
while (a < 10) {
a++;
// code to be executed
}
}
}
``````

In this example, the while loop will execute the code inside the loop until the value of `a` is greater than or equal to 10.

3. Do-While Loop: Solidity also supports `do...while` loops, which are similar to `while` loops but with one key difference: the code inside the loop is guaranteed to execute at least once, regardless of whether the condition is true or false.

The basic syntax for a `do...while` loop is:

``````do {
// code to be executed
} while (condition);
``````

Here’s an example of using a `do...while` loop in Solidity:

``````pragma solidity ^0.8.0;
contract Example {
uint a = 0;
function doWhileLoop() public {
do {
a++;
// code to be executed
} while (a < 10);
}
}``````

## Loop Control

Solidity does not support the traditional `break` and `continue` statements for controlling the flow of a loop. However, there are a few ways to achieve similar functionality in Solidity:

1. Boolean flag: One way to break out of a loop in Solidity is to use a Boolean flag variable. Before the start of the loop, initialize a Boolean flag variable to false. Inside the loop, check the flag variable before each iteration, and if it’s set to true, use a `return` statement to exit the function. Inside the loop, when the desired condition is met, set the flag variable to true, and the loop will exit on the next iteration.
``````pragma solidity ^0.8.0;
contract Example {
function breakExample() public {
bool flag = false;
for (uint i = 0; i < 10; i++) {
if (flag) {
return;
}
if (i == 5) {
flag = true;
}
}
}
}
``````
1. Labeled Break: If you need to break out of multiple nested loops, you can use labeled break statement.
``````pragma solidity ^0.8.0;
contract Example {
function breakExample() public {
outer: for (uint i = 0; i < 10; i++) {
for (uint j = 0; j < 10; j++) {
if(j == 5) {
break outer;
}
}
}
}
}
``````
1. Return: Another way to break out of a loop in Solidity is to use the `return` statement. When the desired condition is met, use a `return` statement to exit the function and return a value if necessary.
``````pragma solidity ^0.8.0;
contract Example {
function breakExample() public {
for (uint i = 0; i < 10; i++) {
if(i == 5) {
return;
}
}
}
}
``````

It’s worth noting that, as with loops in general, it’s important to be mindful of the gas cost when using these techniques to control the flow of a loop, and also to consider alternative ways of achieving the same result, like using a `for` loop with a pre-calculated number of iterations.

Here’s an example of how you might simulate a `break` and `continue` statement in Solidity:

``````pragma solidity ^0.8.0;
contract Example {
function example() public {
for (uint i = 0; i < 10; i++) {
if (i == 5) {
break;
}
if (i % 2 == 0) {
continue;
}
// code to execute
}
}
}
``````

In this example, we’re using a `for` loop to iterate through a range of numbers. Inside the loop, we’re using an `if` statement to check the value of `i`. If `i` is equal to 5, we’re using a `break` statement to exit the loop, otherwise, we’re checking if `i` is even. If `i` is even we’re using a `continue` statement to skip the current iteration of the loop and move on to the next iteration.

It’s important to note that, this code is not actually using `break` and `continue` statements, but rather using a combination of conditional statements, which can help achieve a similar functionality.

It’s also important to be mindful of the gas cost when using these techniques to control the flow of a loop, and also to consider alternative ways of achieving the same result, like using a `for` loop with a pre-calculated number of iterations.

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