解析一下原理！不要代码！

[ 本帖最后由 huangqing 于 2009-11-12 19:04 编辑 ]

这种题很多哦，百度就好了！

#include <iostream>
#include <cstring>
#include <cmath>
using namespace std;

int SToI(const char*& str)
{
    int var = 0;
    int len = 0;
    
    len = strlen(str);
    char c;
    for(int i=0; i<len; ++i)
    {    
        c=str[i];
        var = var*10 + (int)(c-48);
    }
    return var;
}

int main()
{
    const char* str = "12345";
    int var = SToI(str);
    cout << "\"" << str << "\" = " << var << endl;
    return 0;
}

VC++ 6.0 验证通过

#include <iostream>
#include <cstring>
#include <cmath>
using namespace std;

int SToI(const char*& str)
{
    int var = 0;
    int len = 0;
    
    len = strlen(str);
    char c;
    for(int i=0; i<len; ++i)
    {    
        c=str[i];
        var = var*10 + (int)(c-48);
    }
    return var;
}

int main()
{
    const char* str = "12345";
    int var = SToI(str);
    cout << "\"" << str << "\" TO " << var << endl;
    return 0;
}

是数字字符串吗？

是的哦！
 
谢谢楼上的各位！】

#include <iostream>
#include <sstream>
#include <cstdlib>
#include <cstdio>
using namespace std;

int main()
{
    char *str = "12345";
    long n;
    
    n = strtol(str, NULL, 10);
    cout<<"using strtol(), n = "<<n<<endl;
    
    n = strtoul(str, NULL, 10);
    cout<<"using strtoul(), n = "<<n<<endl;
    
    sscanf(str, "%ld", &n);
    cout<<"using sscanf(), n = "<<n<<endl;
    
    stringstream sin;
    sin<<str;
    sin>>n;
    cout<<"using stringstream, n = "<<n<<endl;
    
    return 0;
}

如果是数字字符串可以调用函数：
比如
char str[6]="12345";
int m=atoi(str);atoi()函数将C风格的整型字符串转换成int型
cout<<str;

如果是数字字符串可以调用函数：
比如
char str[6]="12345";
int m=atoi(str);atoi()函数将C风格的整型字符串转换成int型
cout<<str;