Maximum And Minimum With Pointer - c

Question

I tried to run this but it keeps give me zero value. What is wrong in this code?
#include<stdio.h>
main(){
int i,min,max,arr[3]={10,20,40};
int *ptr_arr;
ptr_arr=&arr[3];
for(i=0;i<3;i++){
if(max>*ptr_arr)
max=*ptr_arr;
if(min>*ptr_arr)
min=*ptr_arr;
}
printf("The Maximum Number Is %d\n ",max);
printf("The Minimum Number Is %d ",min);
}

Answer 1

ptr_arr=&arr[3]; // points to index which is beyond no. of index of array
As declaration of arr is arr[3]={10,20,40};so it's valid indexes are 0,1 and 2 .So there is no index 3(array indexing starts with 0).
Also min and max what value does they have ? Uninitialized , so how can your code give correct output.
Make the following changes -
int min=arr[0],max=0;
...
ptr_arr=arr; // points to address of array's first element
And in for loop see condition and increment pointer-
if(max>*ptr_arr) // change condition to max<=*ptr_arr
...
ptr_arr++;
See worning example here-https://ideone.com/r3nv8R

Answer 2

The code misses to initialise min and max to meaningful values.
Do
int min = INT_MAX;
int max = -INT_MAX;
to have the macro above available #include <limits.h>.
ptr_arr gets initialised wrongly to point beyond the array.
Do
int * ptr_arr = arr; /* Here the array "decays" to address of its 1st element. */
or
int * ptr_arr = &arr[0]; /* Explicitly use the address of the array 1st element. */
The code misses to increase ptr_arr to successively access all array's element while looping.
Add
++ptr_arr;
as last statement to the loop.
Also read your code closely to find a nasty typo in comparing.
main() should at least read int main(void).

Answer 3

Just few notes on your code:
you should give min and max an initial value(a value from the array), why? because the initial garbage value might be beyond your array values(say 9999 for example) which yields a wrong result, because your array doesn't have such a value.
Also, im not sure why you need ptr_arr ?
Here is a modified version of your code:
#include<stdio.h>
int main(){
int i,min,max,arr[3]={10,20,40};
max = arr[0]; //initialize 'max' to be the first element of the array
min = arr[0]; //initialize 'min' to be the first element of the array
for(i=0;i<3;i++){
if(arr[i] >= max)
max = arr[i];
if(arr[i] <= min)
min = arr[i];
}
printf("The Maximum Number Is %d\n ",max);
printf("The Minimum Number Is %d ",min);
return 0;
}
Notice also in the if statement i added <= and >=.

Answer 4

Tested and working:
#include <stdio.h>
int main(void) {
int i = 0,min ,max,arr[3]={20,40,10};
int *ptr_arr;
ptr_arr=&arr[0];
min = max = arr[0];
for(i=0;i<3;i++){
if(max < ptr_arr[i]) {
max=ptr_arr[i];
}
if(min>ptr_arr[i]){
min=ptr_arr[i];
}
}
printf("The Maximum Number Is %d\n ",max);
printf("The Minimum Number Is %d ",min);
}
OUTPUT:
The Maximum Number Is 40
The Minimum Number Is 10