Find the number that appears the most in an array - c

Question

I have been debugging this problem for one night but still have no idea what has gone wrong. Let's say I input an array of 6 numbers which is {100,150,150,200,200,250} since 150 and 200 appear the same number of time then output the smaller number.
#include <stdio.h>
#include <stdlib.h>
int main() {
int arr[20] = { NULL }, num, result;
printf("Input a number(1-20) and enter a series of numbers in ascending order: \n");
scanf_s("%d", &num);
for (int k = 0; k < num; k++) {
scanf_s("%d", &arr[k]);
}
int c1, c2, i, j;
int temp = 0;
j = result = 0;
c1 = c2 = 1;
for (i = 1; i <= num-2; i++) { /*Add c1 if the value is the same*/
int a = arr[i];
if (arr[i+1] == a) c1++;
else {
j = i + 1;
temp = arr[j];
while (1) {
if (arr[j+1] == temp) {
c2++;
j++;
}
else break;
}
}
if (c2 > c1) { /*Move i to the position after j*/
c1 = 0;
result = temp;
}
if ((c2 < c1) || (c2 == c1)) { /*Move j to the next position*/
result = a;
c2 = 0;
}
i = j + 1;
}
printf("Number that appears the most time:%d\n", result);
return 0;
}
Will edit everytime after I did some progress
This is what I have done so far.
The output is correct for {100,150,150,200,200,250} but now the loop is stuck if I input a larger array with 8 numbers {100,100,100,150,150,200,250,300}. Help##

Answer 1

The error is in this part:
while (i <= num) { /*Add c1 if the value is the same*/
if (arr[i+1] == a)
Here i should be less than num-1, as you get numbers, the index goes from 0 to num-1, normally i<num would be ok, but you have done i+1 inside the loop so loop must only run from 0 to num-2.
Though, from your logic it should be arr[i] not arr[i+1]
And this part
int a = arr[i];
if (arr[i+1] == a) c1++;
Why would you assign a to value of arr[i] then again check with arr[i+1]? you only get c1 increasing with every duplicate value.
And this part at the end.
i=j+1
which is causing the infinite loop.
This would probably solve your problem although it is not a good solution:
#include <stdio.h>
#include <stdlib.h>
int main() {
int arr[20], num, result;
printf("Input a number(1-20) and enter a series of numbers in ascending order: \n");
scanf("%d", &num);
printf("Now enter the numbers");
for (int k = 0; k < num; k++) {
scanf("%d", &arr[k]);
}
int c1, c2, i, j;
int temp = 0;
j = 0;
result=arr[0];
c2 = 1;
for (i = 0; i < num; i++) { /*Add c1 if the value is the same*/
int a = arr[i];
c1=1;
for(j=i+1;j<num;j++)
{
if (arr[i]==arr[j])
{
c1+=1;
}
}
if(c1>c2)
{
c2=c1;
result=arr[i];
}
else if(c1==c2 && result>arr[i])
{
result=arr[i];
}
}
printf("Number that appears the most time:%d\n", result);
return 0;
}
Other than that, it has a better approach for your problem. make a struct of {int key, int count} then use it to store counts of all unique members in your array, then extract what you need.
Here is the code to what i was saying about, it might be hard to look into if you don't know about pointers & dynamic memory yet. but you'll get the logic.
#include<stdio.h>
#include<stdlib.h>
int main()
{
struct counts
{
int key;
int count;
};
int * data;
int num;
printf("Enter the number of data:");
scanf("%d",&num);
data=malloc(num*sizeof(int));
int i,j;
printf("Enter the data in order:");
for (i=0;i<num;i++)
{
scanf("%d",data+i);
}
struct counts *table;
int table_len=1;
int flag;
table=malloc(sizeof(struct counts));
table[0].key=data[0];
table[0].count=1;
for (i=1;i<num;i++)
{
flag=0;
for(j=0;j<table_len;j++)
{
if (table[j].key==data[i])
{
flag=1;
table[j].count+=1;
break;
}
}
if (flag==0)
{
table=realloc(table,++table_len* sizeof(struct counts));
table[table_len-1].key=data[i];
table[table_len-1].count=1;
}
}
//if you want to see at the table
printf("data\t\tcount\n");
for(i=0;i<table_len;i++)
{
printf(" %d\t\t%d\n",table[i].key,table[i].count);
}
//now to extract the value
int answer,count;
answer=table[0].key;
count=table[0].count;
for(i=1;i<table_len;i++)
{
if(count>table[i].count)
{
continue;
}
else if(count<table[i].count)
{
answer=table[i].key;
count=table[i].count;
}
else if(answer>table[i].key)
{
answer=table[i].key;
}
}
printf("The number with highest frequency is: %d\n",answer);
return 0;
}