In programming, algorithm is a set of well defined instructions in sequence to solve the problem.

- Input and output should be defined precisely.
- Each steps in algorithm should be clear and unambiguous.
- Algorithm should be most effective among many different ways to solve a problem.
- An algorithm shouldn't have computer code. Instead, the algorithm should be written in such a way that, it can be used in similar programming languages.

**Write an algorithm to add two numbers entered by user.**

Step 1: Start Step 2: Declare variables num1, num2 and sum. Step 3: Read values num1 and num2. Step 4: Add num1 and num2 and assign the result to sum. sum←num1+num2 Step 5: Display sum Step 6: Stop

**Write an algorithm to find the largest among three different numbers entered by user.**

Step 1: Start Step 2: Declare variables a,b and c. Step 3: Read variables a,b and c. Step 4: If a>b If a>c Display a is the largest number. Else Display c is the largest number. Else If b>c Display b is the largest number. Else Display c is the greatest number. Step 5: Stop

**Write an algorithm to find all roots of a quadratic equation ax ^{2}+bx+c=0.**

Step 1: Start Step 2: Declare variables a, b, c, D, x1, x2, rp and ip; Step 3: Calculate discriminant D←b2-4ac Step 4: If D≥0 r1←(-b+√D)/2a r2←(-b-√D)/2a Display r1 and r2 as roots. Else Calculate real part and imaginary part rp←b/2a ip←√(-D)/2a Display rp+j(ip) and rp-j(ip) as roots Step 5: Stop

**Write an algorithm to find the factorial of a number entered by user.**

Step 1: Start Step 2: Declare variables n,factorial and i. Step 3: Initialize variables factorial←1 i←1 Step 4: Read value of n Step 5: Repeat the steps until i=n 5.1: factorial←factorial*i 5.2: i←i+1 Step 6: Display factorial Step 7: Stop

**Write an algorithm to check whether a number entered by user is prime or not.**

Step 1: Start Step 2: Declare variables n,i,flag. Step 3: Initialize variables flag←1 i←2 Step 4: Read n from user. Step 5: Repeat the steps until i<(n/2) 5.1 If remainder of n÷i equals 0 flag←0 Go to step 6 5.2 i←i+1 Step 6: If flag=0 Display n is not prime else Display n is prime Step 7: Stop

**Write an algorithm to find the Fibonacci series till term≤1000.**

Step 1: Start Step 2: Declare variables first_term,second_term and temp. Step 3: Initialize variables first_term←0 second_term←1 Step 4: Display first_term and second_term Step 5: Repeat the steps until second_term≤1000 5.1: temp←second_term 5.2: second_term←second_term+first term 5.3: first_term←temp 5.4: Display second_term Step 6: Stop

Algorithm is not the computer code. Algorithm are just the instructions which gives clear idea to you idea to write the computer code.