C++サンプルプログラム

例１）２つの整数の加算

//program file name: ex01.cpp
#include <iostream>
using namespace std;

int main() {
	int a, b, sum;
	cout << "a: ";
	cin >> a;
	cout << "b: ";
	cin >> b;
	sum = a + b;
	cout << "a+b=" << sum << "\n";

	return 0;
}


例２）文字列の読み込みと表示

//program file name: ex02.cpp
#include <iostream>
using namespace std;

int main() {
	char namae[128];

	cout << "Your Name: ";
	cin >> namae;
	cout << "Hello, " << namae << "!\n";

	return 0;
}


（例２の別バージョン）

//program file name: ex02_2.cpp
#include <iostream>
#include <cstring>
using namespace std;

int main() {
	string namae = "";

	cout << "Your Name: ";
	cin >> namae;
	cout << "Hello, " << namae << "!\n";

	return 0;
}


例３）if文による２つの整数の比較

//program file name: ex03.cpp
#include <iostream>
using namespace std;

int main() {
	int a, b;

	cout << "a: ";
	cin >> a;
	cout << "b: ";
	cin >> b;

	if (a < b) {
		cout << "a is less than b.\n";
	} else if (a == b) {
		cout << "a is equal to b.\n";
	} else {
		cout << "a is greater than b.\n";
	}
	return 0;
}

例４）for文による繰り返し

//program file name: ex04.cpp
#include <iostream>
using namespace std;

int main() {
	int n, a;
	cout << "a: ";
	cin >> a;
	for (n=1; n<=a; n++) {
		cout << n << "\n";
	}
	return 0;
}


例４−２）繰り返しによる階乗の計算

//program file name: ex04_2.cpp
#include <iostream>
using namespace std;

int main() {
	int n;
	long a, kaijou;

	cout << "a: ";
	cin >> a;
	kaijou = 1;
	for (n=1; n<a; n++) {
		kaijou *= (n + 1);
	}
	cout << "a!=" << kaijou << "\n";

	return 0;
}


例５）配列変数への数値の入力

//program file name: ex05.cpp
#include <iostream>
using namespace std;

int main() {
	int atai[6];
	int n;

	for (n=1; n<=5; n++) {
		cout << "kotai " << n << ": ";
		cin >> atai[n];
	}
	cout << "\n";
	for (n=1; n<=5; n++) {
		cout << "kotai " << n << ": atai=" << atai[n] << "\n";
	}
	return 0;
}

例５−２）配列変数に数値を入力し，任意の値を呼び出す

//program file name: ex05_2.cpp
#include <iostream>
using namespace std;

int main() {
	int atai[11];
	int n;

	for (n=1; n<=10; n++) {
		cout << "kotai " << n << ": ";
		cin >> atai[n];
	}
	cout << "\n";
	while (1) {	//無限ループ
		cout << "kotai bango: ";
		cin >> n;
		if ((n <= 0) || (10 < n)) break;
		cout << atai[n] << "\n";
	}
	return 0;
}


例６）ファイルへの書き出し

//program file name: ex06.cpp
#include <iostream>
#include <fstream>
using namespace std;

int main () {
	char filename[32], mystr[80];

	cout << "file name: ";
	cin >> filename;	//cin.getline(filename, 31);
	cout << "contents: ";
	cin >> mystr;		//cin.getline(mystr, 79);

	ofstream fout(filename);
	if (!fout) {
		cerr << "Cannot open output file.\n";
		return 1;
	}

	fout << mystr;

	fout.close();

	return 0;
}



例７）ファイルからの読み込み

//program file name: ex07.cpp
#include <iostream>
#include <fstream>
using namespace std;

int main () {
	char filename[32], mystr[80];

	cout << "file name: ";
	cin >> filename;

	ifstream fin(filename);
	if (!fin) {
		cout << "Cannot open output file.\n";
		return 1;
	}

	fin >> mystr;		//fin.getline(mystr, 79);

	fin.close();

	cout << mystr << "\n";

	return 0;
}