将数字字符串中字符转换为整数并返回其值

#include<stdio.h>int ascii_to_integer(char *str)  {      int n = 0;      int sum = 0;        while(*str != '\0')      {         if( (*str)<'0' || (*str)>'9' )  {  return 0;}       else{  n = *str - '0';           sum = sum * 10 + n;            str++;}    }       return sum;    }  int main(){   char *p = "1234";     printf("%d\n",ascii_to_integer(p));   return 0;}