c - int i in a for loop vs not -

why following not work when defined in loop

#include <stdio.h> #include <math.h> int n; long long int h() {      long long int ans=0;     int i, lt;      if(n <= 0)         return 0;      for(i=1, lt=sqrt(n); i<=lt; i+=1) /* if i=1 replaced int i=1 => garbage */         ans+=(n/i);      ans = 2*ans-(lt*lt);     return ans;  } int main() {      scanf("%d",&n);     printf("%lld\n",h());      return 0; } 

output when it's defined @ top

input: 8 output: 20 

output when it's defined in loop /* (int i=1 ..) */

input: 8 output: 1243068212 

i see warning lt initialized when used here, why?

when write this:

int lt; (int i=1, lt=sqrt(n); ...) 

that defines two new inner variables named i , lt; in particular, new lt variable shadows outer one, making temporarily inaccessible within inner scope. so, outer lt variable never gets initialized, , when compute ans = 2*ans-(lt*lt), it's using uninitialized value compute result.