C C++ programming C语言 编程 语言 教學

getchar()、putchar()：

#include < cstdio >
#include < cstdlib >

int main() {
    printf("請輸入一個字元：");
    char c = getchar();
    putchar(c);
    putchar('\n');
    system("PAUSE");
    return 0;
}

getchar()取得使用者輸入的字元，putchar()輸出一個字元。

gets()、puts()：
gets()會取得使用者的輸入字串，不包括按下Enter的換行字元碼，puts()用來輸出字串，並直接進行換行。

#include < cstdio >
#include < cstdlib >

int main(void) {
    char str[20];
    puts("請輸入字串：");
    gets(str);
    puts("輸入的字串為：");
    puts(str);
    system("PAUSE");
    return 0;
}

格式控制器、格式旗標(cout)

cout有預設的輸出格式，也可以自行指定格式，像endl就是格式控制器的一種，它會輸出new line字元至串流中，格式控制器只會影響目前正在處理的串流，串流處理結束後即回復成預設的格式，格式控制器也可以指定參數，如果要使用具有參數的格式控制器，必須含入iomanip這個標頭檔案，下面為簡單的使用。

#include <iostream> 
#include <iomanip>
using namespace std;

int main() {
    cout << oct << 30 << endl;    //8進位顯示 
    cout << hex << 30 << endl;    //16進位顯示 
    cout << setw(2) << 5 << endl; //寬度為2
    system("PAUSE");
    return 0;
}

---

格式控制器可以改變目前的串流格式，如果想要讓所有的串流都維持特定格式，可以使用格式化旗標，使用setf()與unsetf()來設定與取消格式化旗標，下面為簡單的示範。

#include <iostream> 
using namespace std;

int main() {
    cout.unsetf(ios::dec);              
    cout.setf(ios::hex); 
    cout << 120 << endl;
    cout << 50 << endl;

    cout.setf(ios::dec);
    cout.setf(ios::scientific);
    cout << 50.25 << endl;

    system("PAUSE");
    return 0;
}

Basic types of Variables

Each variable while declaration must be given a datatype, on which the memory assigned to the variable depends. Following are the basic types of variables,

bool	For variable to store boolean values( True or False )
char	For variables to store character types.
int	for variable with integral values
float and double are also types for variables with large and floating point values

Declaration and Initialization

Variable must be declared before they are used. Usually it is preferred to declare them at the starting of the program, but in C++ they can be declared in the middle of program too, but must be done before using them.

For example:

int i;      // declared but not initialised
char c; 
int i, j, k;  // Multiple declaration

Initialization means assigning value to an already declared variable,

int i;   // declaration
i = 10;  // initialization

Initialization and declaration can be done in one single step also,

int i=10;         //initialization and declaration in same step
int i=10, j=11;

If a variable is declared and not initialized by default it will hold a garbage value. Also, if a variable is once declared and if try to declare it again, we will get a compile time error.

int i,j;
i=10;
j=20;
int j=i+j;   //compile time error, cannot redeclare a variable in same scope