Why variable b don't change in the for-loop? [closed] - c

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Hy, I want to understand why variable b don't change and when I print it always be as I defined (zero). What's wrong with my code??
With this code I want to find the max integer number (b) that is 10^b <= n (with n given and integer as well).
This is my code (It's written in c):
#include <stdio.h>
#include <math.h>
int lg (int n);
int main() {
int a = 0;
scanf("%d", &a);
printf ("\nN=%d e M=%d\n", a, lg(a));
return 0;
}
int lg (int n) {
double b = 0.0;
for (int i=0; i==n; i++) {
if (pow(10, i) <= n) {
double b = i;
} else {
}
}
return (int)b;
}

Answer 1

You're declaring a new variable named b inside your loop and setting it equal to i. Since that's a different scope, it's not the same variable as the b declared before the loop. Change the line
double b = i;
to
b = i;
Your loop condition is also set to i==n;. That means your loop will only run once if your input is 0. That should probably be i < n;.

Answer 2

There are two variables named b. One whose scope is the function lg, and one whose scope is restricted to the if clause of the for loop. You modify the latter, but return the former. Using the keyword 'double' declares a new varaible. This is a common source of error, and simply turning up the warnings on your compiler should alert you to the problem.

Answer 3

You are declaring "b" variable twice.The "b" variable initialized with 0.0 have scope within the function "lg". And the "b" declared inside if codition have limited scope to that condition only.
Also check the second parameter of for loop i.e "i==n". This is statement would be always true i.e "1" if the value of input ("n") is not zero.

Answer 4

Error 1: i==n: if you compare i==n in a for loop, that loop will only run a time.You must fix it into i<n
Error 2: You repeated a double type. You mustn't declare a variable b in a for loop because the variable b in that loop will disappear from the loop when it stop repeating.Thus, the value of the variable b in the for loop won't assign.
You must delete the double keyword in the for loop, the variable b will change.