**C++ programs to calculate the percentage of a number** have been given below. A percentage is represented as a number or a ratio which is a fraction of 100. It is denoted by the symbol '%'. For example 25% represents (25 / 100) or 0.25. So, 25% of a number *b* will be calculated as *b* * (25 / 100) or *b* * 0.25.

Suppose *a* and *b* are two numbers. Then, the solution to the percentage problem is obtained by answering any of the following queries.

(i) What is *a*% of *b*?

(ii) *a* is what % of *b*?

(iii) *a* is *b*% of what?

Let's assume *a* = 15 and *b* = 60, then the solutions w.r.t the above queries:

(i) ___ is *a*% of *b* := 15% of 60 := 60 * (15 / 100) := 9

(ii) *a* is ___ % of *b* := (15 / 60) * 100 := 25%

(iii) *a* is *b*% of ___ := (15 / 60) * 100 := 25

In the following section, C++ programs to solve the above problems are given along with the algorithm, pseudocode and time-complexity of the programs.

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## 1. Algorithm to calculate percentage of a number

1. Take a number *a* as input.

2. Take another number *b* as input where b% of a is to be calculated.

3. Calculate *a * (b / 100)* and declare it as the output.

## 2. Pseudocode to calculate percentage of a number

**Input** : Two numbers a, b

**Output** : b% of a

1. **Procedure** percentage(a, b):

2.

3. **Return** x

4. **End Procedure**

## 3. Time complexity to calculate percentage of a number

**Time Complexity: O(1)**

## 4. Programs to calculate percentage

## 4.1. C++ Program to calculate "What is a% of b?"

/**************************************** alphabetacoder.com C++ program to calculate what is a% of b? *****************************************/ #include <iostream> #include <iomanip> using namespace std; int main() { // declare variables float a, b, x; // take input cout << "Enter values to calculate a% of b" << endl; cout << "Enter a = "; cin >> a; cout << "Enter b = "; cin >> b; // calculate value x = b * (a / 100); // display result upto 3 decimal places cout << fixed << setprecision(3) << x << " is " << a << "% of " << b << endl; return 0; }

Output

**Case 1:**

Enter values to calculate a% of b

Enter a = 65

Enter b = 150

97.500 is 65.000% of 150.000

**Case 2:**

Enter values to calculate a% of b

Enter a = 200

Enter b = 20

40.000 is 200.000% of 20.000

## 4.2. C++ Program to calculate "a is what % of b?"

/***************************************** alphabetacoder.com C++ program to calculate a is what % of b? ******************************************/ #include <iostream> #include <iomanip> using namespace std; int main() { // declare variables float a, b, x; // take input cout << "Enter values to calculate a is what % of b?" << endl; cout << "Enter a = "; cin >> a; cout << "Enter b = "; cin >> b; // calculate value x = (a / b) * 100; // display result upto 3 decimal places cout << fixed << setprecision(3) << a << " is " << x << "% of " << b << endl; return 0; }

Output

**Case 1:**

Enter values to calculate a is what % of b?

Enter a = 10

Enter b = 30

10.000000 is 33.333% of 30.000000

**Case 2:**

Enter values to calculate a is what % of b?

Enter a = 30

Enter b = 45

30.000000 is 66.667% of 45.000000

## 4.3. C++ Program to calculate "a is b% of what?"

/***************************************** alphabetacoder.com C++ program to calculate a is b% of what? ******************************************/ #include <iostream> #include <iomanip> using namespace std; int main() { // declare variables float a, b, x; // take input cout << "Enter values to calculate a is b % of what?" << endl; cout << "Enter a = "; cin >> a; cout << "Enter b = "; cin >> b; // calculate value x = (a / b) * 100; // display result upto 3 decimal places cout << fixed << setprecision(3) << a << " is " << b << "% of " << x << endl; return 0; }

Output

**Case 1:**

Enter values to calculate a is b % of what?

Enter a = 13

Enter b = 35

13.000 is 35.000% of 37.143

**Case 2:**

Enter values to calculate a is b % of what?

Enter a = 16.66

Enter b = 75

16.660 is 75.000% of 22.213