**Discussion 3**
09/08, 09/10
[(back to course webpage)](./mcs360_fall2020.html)
# Problem 1
Write a CPP program that asks the user to input a number $n$, and then input $n$ integers $a_0,\ldots,a_{n-1}$. Store these integers in a `std::vector` object. Then, find the largest number in the integers.
## Example Run:
```
Enter n: 5
Enter the integers: 100 200 30 50 70
The largest integer is: 200
```
## Hints
Hint 1
This is how you would take the input:
~~~~~~~~cpp
int main() {
int n;
std::cout << "Enter n: ";
std::cin >> n;
std::vector a;
std::cout << "Enter the integers: ";
int inp;
for(int i = 0; i < n; i++) {
std::cin >> inp;
a.push_back(inp);
}
// Find the largest!
return 0;
}
~~~~~~~~~
Now your job is to figure out an algorithm to compute the largest entry!
Hint 2
We can find the largest in the array by the following algorithm:
**********************************************************************************************************************************************
*|100|200| 30| 50| 70| |100|200| 30| 50| 70| |100|200| 30| 50| 70| |100|200| 30| 50| 70| *
* ^ ^ ^ ^ *
* | -> | -> | -> ... -> | *
* i=0 i=1 i=2 i=4 *
* (initial) (100 < 200) (200 > 30) (200 > 70) *
* l=100 l=200 l=200 l=200 *
**********************************************************************************************************************************************
## Solution
Solution
~~~~~~~~~~cpp
#include
#include
int main() {
int n;
std::cout << "Enter n: ";
std::cin >> n;
std::vector a(n); // same thing as saying int a[n];
std::cout << "Enter the integers: ";
for(int i = 0; i < n; i++) {
std::cin >> a[i];
}
// Find the largest!
int largest = a[0];
for(int i=1; i < n; i++) {
if(largest < a[i]) {
largest = a[i];
}
}
// Is it possible to find the largest in less than n number of primitive steps?
// The answer is no: you have to at least loop through all the elements of the array
// once, otherwise it's impossible to figure out the largest of them.
std::cout << "The largest integer is: " << largest << std::endl;
return 0;
}
~~~~~~~~~~~~
Remark
There is also a standard library function called `std::max_element` in `algorithm.h` that lets you do this in a click, but it does exactly what we did here.
Check [here](https://www.cplusplus.com/reference/algorithm/max_element/) for the details.
# Problem 2
Write a CPP program that populates an `std::vector` with 100 random numbers, each ranging from 0 to 9 (both inclusive).
Print the elements of the vector.
Find the element with the highest frequency in the vector.
## Hints
Hint 1
You can look up the rolling die problem done in lecture. It tells you how to compute the frequency of every element.