To solve the problem, we can use an array. Whenever an element is entered, the corresponding subscript will be added. It may be a bit difficult to understand here, so let's give a small example to understand.
eg: 
The array is all initialized to 0, if n=3, then arr[n]++, then arr[3] becomes 1, if arr[n]+=2, then arr[3] ] into 3, we use this relationship to store the number of times each number is entered.
Note: The title requires the output with the most occurrences, and there may be multiple inputs with the most repetitions. So pay attention to traversing the array.
Compiler: VS2019;
Source code:
int main()
{ int arr[100] = { 0 }; int i = 0; int max = arr[0]; while (scanf_s(“%d”,&i)&&i >= 0)//Input -1 to end, every time i is input, arr[i]++ will be generated; { arr[i]++;
}
for (i = 0; i < 100; i++)//找到最大值
{
if (arr[i] > max)
{
max = arr[i];
}
}
for ( i = 0; i < 100; i++)//将最大值打印输出，可能会有重复的，所以对100个进行遍历。
{
if (arr[i] == max)
{
printf("%d ", i);
}
}
return 0;
}