C++ practical

file organization

#include <iostream>

float distance(float velocity, float acceleration, float time_elapsed);

int main() {

    std::cout << distance(3, 4, 5) << std::endl;  
    std::cout << distance(7.0, 2.1, 5.4) << std::endl;

    return 0;   
}

float distance(float velocity, float acceleration, float time_elapsed) {
    return velocity*time_elapsed + 0.5*acceleration*time_elapsed*time_elapsed;
}

分成多个文件

1. main.cpp and distance.cpp

//#main.cpp
#include <iostream>

float distance(float velocity, float acceleration, float time_elapsed);

int main() {

    std::cout << distance(3, 4, 5) << std::endl;  
    std::cout << distance(7.0, 2.1, 5.4) << std::endl;
    
    return 0;   
}

//distance.cpp
float distance(float velocity, float acceleration, float time_elapsed) {
    return velocity*time_elapsed + 0.5*acceleration*time_elapsed*time_elapsed;
}

2. 头文件： main.cpp and distance.cpp and distance.h
   头文件放函数申明

// 头文件 distance.h

float distance(float velocity, float acceleration, float time_elapsed);

// main.cpp
#include <iostream>
#include "distance.h"

int main() {

    std::cout << distance(3, 4, 5) << std::endl;  
    std::cout << distance(7.0, 2.1, 5.4) << std::endl;
    
    return 0;   
}

// distance.cpp
float distance(float velocity, float acceleration, float time_elapsed) {
    return velocity*time_elapsed + 0.5*acceleration*time_elapsed*time_elapsed;
}

reading in the Text Files

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
#include <vector>

using namespace std;

int main() {

    // initialize string variables for reading in text file lines 
    string line;
    stringstream ss;

    // initialize variables to hold the matrix
    vector < vector <float> > matrix;
    vector<float> row;

    // counter for characters in a text file line
    float i;

    // read in the file
    ifstream matrixfile ("matrix.txt");

    // read in the matrix file line by line
    // parse the file

    if (matrixfile.is_open()) {
        while (getline (matrixfile, line)) {
//getline() 读取每一行，每行都放在名为" line"的变量中
            // parse the text line with a stringstream
            // clear the string stream to hold the next line
            ss.clear();
            ss.str("");
            ss.str(line);
            row.clear();

            // parse each line and push to the end of the row vector
            while(ss >> i) {
                row.push_back(i);

                if (ss.peek() == ',' || ss.peek() == ' ') {
// ss.peak() 查看下一个字符
                    ss.ignore();
                }
            }

            // push the row to the end of the matrix
            matrix.push_back(row);
        }

        matrixfile.close();

        // print out the matrix
        for (int row = 0; row < matrix.size(); row++) {
            for (int column = 0; column < matrix[row].size(); column++) {
                cout << matrix[row][column] << " " ;
            }
            cout << endl; 
        }
    }

    else cout << "Unable to open file";

    return 0;
}

// matrix.txt
1, 6, 2, 10.5
11, 15.2, 2, 21
3, 9, 1, 7.5

输出到文本文件

#include <iostream>
#include <fstream>
#include <vector>

using namespace std;

int main() {

    // create the vector that will be outputted
    vector < vector <int> > matrix (5, vector <int> (3, 2));
    vector<int> row;

    // open a file for outputting the matrix
    ofstream outputfile;
    outputfile.open ("matrixoutput.txt");

    // output the matrix to the file
    if (outputfile.is_open()) {
        for (int row = 0; row < matrix.size(); row++) {
            for (int column = 0; column < matrix[row].size(); column++) {
                if (column != matrix[row].size() - 1) {
                    outputfile << matrix[row][column] << ", ";
                }
                else {
                    outputfile << matrix[row][column];
                }//if语句正在检查是否到达行的末尾。如果当前值是行的结尾，则不必在数字后面加上逗号分隔符：
            }
            outputfile << endl; 
        }
    }

    outputfile.close();

    return 0;
}