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StringtoInteger.c
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#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<stdbool.h>
#include<math.h>
int myAtoi(char *s)
{
int begin = -1;
bool flag = 0;
while (s[++ begin] == ' ');
if (s[begin] == '-' || s[begin] == '+')
{
flag = s[begin] == '+' ? 0 : 1;
++ begin;
}
if (s[begin] < '0' || s[begin] > '9') return 0;
while (s[begin ++] == '0');
if (s[-- begin] < '0' || s[begin] > '9') return 0;
int end = begin;
while (s[++ end] >= '0' && s[end] <= '9');
int out = 0, base = 1, check = end - begin;
if (check > 10) return flag ? -2147483648 : 2147483647;
int a[10] = {2, 1, 4, 7, 4, 8, 3, 6, 4, 7};
if (flag) a[9] = 8;
if (check == 10)
for (int i = begin; i < end; ++ i)
{
if (s[i] - '0' > a[i - begin])
return flag ? -2147483648 : 2147483647;
if (s[i] - '0' < a[i - begin]) break;
if (i == end - 1 && s[i] - '0' == a[9])
return flag ? -2147483648 : 2147483647;
}
for (int i = end - 1; i >= begin; -- i)
{
out += base * (s[i] - '0');
if (!-- check) break;
base *= 10;
}
return flag ? -out : out;
}
int main()
{
FILE *fin = fopen("oo.xx", "r");
FILE *fout = fopen("xx.oo", "w");
char s[201];
fscanf(fin, "%s", s);
int out = myAtoi(s);
printf("%d\n", out);
fprintf(fout, "%d\n", out);
return 0;
}