编程之美 焦距

<span style="font-size:18px;">#include <iostream>#include <fstream>#include <string>using namespace std;double change(string s) {    //cout<<s<<endl;    double value;    if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) == 'd') {        // dm        value = atof(s.substr(0,s.length()-2).data());        value *= 100;    }else if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) == 'c') {        // cm        value = atof(s.substr(0,s.length()-2).data());        value *= 10;    }else if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) == 'm') {        // mm        value = atof(s.substr(0,s.length()-2).data());    }else if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) == 'u') {        // um        value = atof(s.substr(0,s.length()-2).data());        value /= 1000;    }else if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) == 'n') {        // nm        value = atof(s.substr(0,s.length()-2).data());        value /= 1000*1000;    }else if(s.at(s.length()-1) == 'm' && s.at(s.length()-2) != 'm') {        // m        value = atof(s.substr(0,s.length()-1).data());        value *= 1000;    }else {        // px        value = atof(s.substr(0,s.length()-2).data());    }    return value;}int main(int argc, const char * argv[]) {    ifstream in("/Users/urey/data/input");    int T;    in >> T;    for (int i = 0; i < T; ++i){        string s1,s2,s3;        in>>s1>>s2>>s3;        double ff = change(s1);        double cc = change(s2);        double ii = change(s3);        double result = ii * ff / cc;        cout<<"Case "<<i+1<<": ";        cout.setf(ios::fixed);        cout.precision(2);        cout<<result<<endl;    }    return 0;}</span>

（1）string转数值型，比如string转double，atof

（2）string转const char*，string.data()

（3）保留两位小数：cout.setf(ios::fixed)，cout.precision(2);