c lang atoi

atoi.c

#include "atoi.h"

int main (int argc, char* argv[]) {
  printf("%d\n", atoi(argv[1]));
  return 0;
}

atoi.h

#include <stdio.h>

int atoi (char str[]) { //with negative digits processing
  int number = 0;
  if (  ( (int)(*str) == 45 )  ) {
    str++;
    while(*(str) != '\0') {
      if (  ( (int)(*(str)) >= 48 ) && ( (int)(*(str)) <= 57 )  ) {
        number = number*10 + (*str) - '0';
      } else {
        return 0;
      }
      str++;
    }
    return number*(-1);
  } else {
    while(*(str) != '\0') {
      if (  ( (int)(*(str)) >= 48 ) && ( (int)(*(str)) <= 57 )  ) {
        number = number*10 + (*str) - '0';
      } else {
        return 0;
      }
      str++;
    }
    return number;
  }
}

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