Getting maximum value from array in C++ using pointer - c++

Question

I am gonna want maximum value from the array using a pointer. But I am not getting the accurate value. Please, help.
#include <iostream>
using namespace std;
int main()
{
int* largest;
int a[5]={4,5,666,7,8};
largest=a;
for(int i=1; i<5; i++)
{
if(*largest<*(largest+i))
{
*largest=*(largest+i);
largest=largest+i;
}
}
cout<<*largest;
}
I am getting 7339544 as an output rather than 666. I don't know what I am doing wrong.

Answer 1

You're indexing outside the array, causing undefined behaviour.
You're doing this
largest
|
v
| 4 | 5 | 666 | 7 | 8 |
^
|
largest + 1
then
largest
|
v
| 5 | 5 | 666 | 7 | 8 |
^
|
largest + 2
then
largest
|
v
| 5 | 7 | 666 | 7 | 8 | outside
^
|
largest + 3
(Note that you're also modifying the array, which you shouldn't.)
The main problem is that you're trying to use largest for three purposes simultaneously:
iterating,
storing the largest value,
storing the position of the largest value.
It should only point to the largest array element; you should only change its value, not the value of the element it points to.
int main()
{
const int a[5] = {4, 5, 666, 7, 8};
const int* largest = a;
for (int i = 1; i < 5; i++)
{
if (*largest < a[i])
{
largest = &a[i];
}
}
cout << *largest;
}

Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int generateNumber(int lower_limit, int upper_limit);
void fillArr(int *arr, unsigned int arrSize, int lower_limit, int upper_limit);
void printElementsArr(int *arr, unsigned int arrSize);
int maxElementArr(int *arr, unsigned int arrSize);
int main()
{
char expression;
int l_l, u_l;
int arrSize;
do{
srand(time(0));
printf("Insert array size:\n");
scanf("%d", &arrSize);
if(arrSize < 0){
while (arrSize<0){
printf("Insert positive array size:\n");
scanf("%d", &arrSize);
}
}
int array[arrSize];
printf("Insert lower limit of an array:\n");
scanf("%d", &l_l);
printf("Insert upper limit of an array:\n");
scanf("%d", &u_l);
while(u_l<l_l){
printf("the upper limit (%d) is smaller then the lower limit (%d), set a new upper limit of an array: ",u_l,l_l);
scanf("%d",&u_l);
}
fillArr(array, arrSize, l_l, u_l);
printElementsArr(array, arrSize);
maxElementArr(array, arrSize);
getchar();
printf("If you want to end the program insert 'n' else insert any key: ");
scanf("%c",&expression);
}while(expression != 'n');
}
//---------------------------------------------------------------------------------------------------------
int generateNumber(int lower_limit, int upper_limit){
return rand() % (upper_limit-lower_limit)+lower_limit;
}
void fillArr(int *arr, unsigned int arrSize, int lower_limit, int upper_limit){
int i = 0;
for (i; i < arrSize; i++){
*(arr+i)= generateNumber(lower_limit, upper_limit);
}
}
void printElementsArr(int *arr, unsigned int arrSize){
int i = 0;
printf("\n");
for (i; i < arrSize; i++){
printf("%d.element of an array: %d\n" ,i+1, *(arr+i));
}
}
int maxElementArr(int *arr, unsigned int arrSize){
int i = 1, max= *arr;
for(i; i<arrSize; i++){
if(max < *(arr+i)){
max = *(arr+i);
}
}
printf("\nThe max element of an array is: %d\n",max);
}
Because this code consists of multiple parts I created each independent functions for each problem a then I initially called them in my main function except the one that generates numbers. I used that one in the function where it fills the array with the numbers.
I created the function for generating a random numbers, filling an array with the numbers and printing every each element(number) of an array.
The reason I created the random number generator is because it is more dynamic than static array with pre-defined numbers and size of an array.
Also before the fill and print functions are called, first I ask the user for an array size and if the array size is lower than 0 therefore it will ask the user to insert a positive number and a I also ask user for a lower and an upper limit of an array and if the upper limit is lower than the lower limit a question with the information that the upper limit is lower than the upper one will pop-up over and over again with the option to insert a new upper limit unless the user inserts a number that is higher than the lower limit.
Also, the whole program is in loop with the question in the end if they want to end the program.

Answer 3

#include <iostream>
using namespace std;
int main()
{
int* largest;
int a[5]={4,5,666,7,8};
largest=a;
for(int i=1; i<5; i++)
{
if(*largest < a[i])
{
largest = &a[i];// This works perfectly
//largest = largest+i; There is no meaning of this line
}
}
cout<<*largest;
}