Segfault when creating an array larger than 100000 [duplicate] - c

Question

This question already has answers here:
Getting a stack overflow exception when declaring a large array
(8 answers)
Closed 3 years ago.
How can I fix this code? I can't input a value for n more than 100000 but I have declared it as long long int.
I tried to solve it but couldn't. Please tell me what is wrong.
#include<stdio.h>
void main() {
long int n;
scanf("%ld",&n);
unsigned long long int a[n];
unsigned long long int max[n];
for(unsigned long long int i=0;i<n;i++) {
scanf("%lld",&a[i]);
}
for(unsigned long long int i=0;i<n;i++) {
unsigned long long int count=0;
for(unsigned long long int j=0;j<n;j++) {
if(a[i]==a[j]) {
count++;
}
}
max[i]=count;
}
for(unsigned long long int i=1;i<n;i++) {
if(max[0]<max[i]) {
max[0]=max[i];
a[0]=a[i];
}
else if(max[0]==max[i]) {
if(a[0]>a[i]) {
a[0]=a[i];
}
}
}
printf("%lld",a[0]);
}

Answer 1

You're declaring variables on the stack that are too big:
unsigned long long int a[n];
unsigned long long int max[n];
These variables are declared local to the function main, meaning that on most implementations they live on the stack. The stack is typically not that big, so when you specify a large value for n it creates arrays on the stack that are too big, overflowing the stack and causing a segfault.
Rather than creating the arrays on the stack, use malloc to create them on the heap:
unsigned long long int *a = malloc(n * sizeof(*a));
unsigned long long int *max = malloc(n * sizeof(*a));
Also, make sure you check the return value of malloc and call free when you're done.