foo.c: In function 'main':
foo.c:8:21: warning: implicit declaration of function 'pow' [-Wimplicit-function-declaration]
    8 |                 b = pow(2, d - 1 - i);
      |                     ^~~
foo.c:2:1: note: include '<math.h>' or provide a declaration of 'pow'
    1 | #include <stdio.h>
  +++ |+#include <math.h>
    2 | int main() {
foo.c:8:21: warning: incompatible implicit declaration of built-in function 'pow' [-Wbuiltin-declaration-mismatch]
    8 |                 b = pow(2, d - 1 - i);
      |                     ^~~
foo.c:8:21: note: include '<math.h>' or provide a declaration of 'pow'
foo.c:7:24: warning: 'i' is used uninitialized [-Wuninitialized]
    7 |                 a = str[i] - 48;
      |                     ~~~^~~

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