Program to calculate sum of numbers from m to n.

• Hint: Input two numbers m and n. Find sum of all numbers from m to n. For example m=3 and n=8 then sum will be 3 + 4 + 5 + 6 + 7 + 8 = 33.

Use for loop or while to solve it.

I make a mistake here, because of "=" and "==".

Program to print Fibonacci series up to 100.

• Hint: Fibonacci Series is 1, 1, 2, 3, 5, 8, 13, 21, ....

Integer Overflow:

If two number too large, the sum of them maybe to a negative number. It means the result affects the symbolic representation of the first bit.

Program to input a number and then calculate sum of its digits.

• Hint: let number = 562. Then you should print 5 + 6 + 2 = 13.

#include isdigit()

The functions determine whether the character is an integer.

Using mod to get a last number of a integer

sum = sum + a % 10;

a = a / 10;

static_cast

int num = static_cast(c - '0');

The function will cast character c to a ASCII value like 5 is "53".

Program to find whether given number is a prime number or not.

Program to display sum of series 1 + 1/2 + 1/3 + ... + 1/n.

Program to display series and find sum of 1 + 3 + 5 + ... + n.

Program to use switch statement. Display Monday to Sunday.

Cin.clear and Cin.ignore

if our cin input can's cast correctly like

int day;

cin>>day; //day is "cscac"

it means our cin will into a fail state.

We need to clear the state and remind user to enter correctly, and then clear the values we don't want.

cin.clear();

cin.ignore(std::numeric_limits< std::streamsize >::max(), '\n'); //ignore all values until to the "\n"

Special case:

If we have a day input which is integer, and we enter a float value(3.2), the cin will get the input 3 first and leave the .2 into the string buffer. So it means in the next cin input, we are going to handle the input ".2"

	if (!(cin >> day)) { 
//if the input is 2.3, it will enter the correct state first and then enter the fail state, 2 will cast correctly, .3 will enter the false state
			cout << day << endl;
			cin.clear();
			cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
			cout << "It's fail state" << endl;
		}
		else {
			cout << day << endl;
			cout << "It's correct state" << endl;
		}

	if (!(cin >> day0)) { 
	//the string buffer have a .2, so it will into the fail state.
			cout << day0 << endl;
			cin.clear();
			cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
			cout << "It's fail state" << endl;
		}
		else {
			cout << day0 << endl;
			cout << "It's correct state" << endl;
		}

Program to display arithmetic operator using switch case

When we use cin to get input from keyboard, we will get input by type. Like cin>>char op, if we enter asasdad, we will get a first and leave the sasdad to the next cin.