1. require:

• a validator function which takes two parameter, 1st the condn and second is the msg to display if error occurs
• e.g

function divide(uint _numberOne, uint _numberTwo) public returns (uint) {
	require(_numberOne && numberTwo > 0, "number should be greater than 0");
	return _numberOne / _numberTwo;
}

2. for loop:

• simple iterative loop
• e.g.

function sum(uint[] _nums) public returns (uint){
	uint ans = 0;
	for(uint i = 0; i < _nums.length; i++){
		ans += _nums[i]
	}
	return ans;
}

3. If-else:

function checkEven(uint _num) public returns (bool){
	if(_num % 2 == 0){
		return true;
	} else {
		return false;
	}
}