1073 Scientific Notation (20)

Scientific notation is the way that scientists easily handle very large numbers or very small numbers. The notation matches the regular expression [+-][1-9]"."[0-9]+E[+-][0-9]+ which means that the integer portion has exactly one digit, there is at least one digit in the fractional portion, and the number and its exponent's signs are always provided even when they are positive.

Now given a real number A in scientific notation, you are supposed to print A in the conventional notation while keeping all the significant figures.

Input Specification:

Each input file contains one test case. For each case, there is one line containing the real number A in scientific notation. The number is no more than 9999 bytes in length and the exponent's absolute value is no more than 9999.

Output Specification:

For each test case, print in one line the input number A in the conventional notation, with all the significant figures kept, including trailing zeros,

Sample Input 1:

+1.23400E-03

Sample Output 1:

0.00123400

Sample Input 2:

-1.2E+10

Sample Output 2:

-12000000000

 

 题目：把科学计数法的表达式转化为10进制的表达式

思路：先找出小数点后面有效数字位数， 找出指数， 根据指数的正负修改字符串， 得到最终答案

#include<iostream>
#include<string>
using namespace std;
int main(){
  string s;
  int i;
  cin>>s;
  bool isPositive= s[0]=='+' ? true : false;
  bool positiveExp = true, findE=false;
  int dot, pos, exp=0;
  //找小数点， E的位置， 以及计算指数值
  for(i=1; i<s.size(); i++){
    if(s[i]=='.') dot = i;
    if(s[i]=='E'){
      pos = i;
      if(s[i+1]=='-') positiveExp=false;
      findE=true;
    }
    if(findE && s[i]>='0'&&s[i]<='9') exp = exp*10 + (s[i]-'0');
  }
  //依次删除小数点， E以及E之后的字符串， 符号位
  //位置不可交换， 否则会出错， 剩下的全是数字位
  s.erase(dot, 1);  s.erase(pos-1); s.erase(0,1);
  if(positiveExp){
    if(exp<pos-dot-1) s = s.substr(0, exp+1) + "." + s.substr(exp+1);
    else{
      for(i=0; i<-pos+dot+1+exp; i++) s.append("0");
    }
  }else{
    string temp="";
    for(i=0; i<exp-1; i++) temp.append("0");
    s = "0." + temp + s.substr(0);
  }
  if(!isPositive) cout<<'-';
  cout<<s<<endl;
  return 0;
}