📜  C / C++ For循环与示例

📅  最后修改于: 2021-05-30 15:16:28             🧑  作者: Mango

当我们需要重复执行一个语句块时,就会使用C / C++中的循环

For循环是一种重复控制结构,它使我们可以编写执行特定次数的循环。该循环使我们可以在一行中一起执行n个步骤。

句法:

for (initialization expr; test expr; update expr)
{    
     // body of the loop
     // statements we want to execute
}

For循环的各个部分是:

  1. 初始化表达式:在此表达式中,我们必须将循环计数器初始化为某个值。
    例子:
    int i=1;
  2. 条件:在此表达式中,我们必须测试条件。如果条件的计算结果为true,那么我们将执行循环的主体并更新表达式。否则,我们将从for循环中退出。
    例子:
    i <= 10
  3. 更新表达式:执行循环主体后,此表达式将循环变量增加/减少一些值。
    例子:
    i++;

For循环如何执行?

  1. 控制进入for循环。初始化完成
  2. 流程跳至条件
  3. 条件已测试。
    1. 如果“条件”为真,则流进入身体
    2. 如果Condition的结果为false,则流程进入循环之外
  4. 循环体内的语句将被执行。
  5. 流程进入更新
  6. 进行更新,流程再次转到步骤3
  7. for循环已结束,流程已流出。

循环流程图(用于控制流):

示例1:该程序将尝试打印5次“ Hello World”。该程序将以以下方式执行:

C
// C program to illustrate for loop
  
#include 
  
int main()
{
    int i = 0;
  
    // Writing a for loop
    // to print Hello World 5 times
    for (i = 1; i <= 5; i++) {
        printf("Hello World\n");
    }
  
    return 0;
}


C++
// C++ program to illustrate for loop
  
#include 
using namespace std;
  
int main()
{
  
    // Writing a for loop
    // to print Hello World 5 times
    for (int i = 1; i <= 5; i++) {
        cout << "Hello World\n";
    }
  
    return 0;
}


C
// C program to illustrate for loop
  
#include 
  
int main()
{
    int i = 0;
  
    // Writing a for loop
    // to print odd numbers upto N
    for (i = 1; i <= 10; i += 2) {
        printf("%d\n", i);
    }
  
    return 0;
}


C++
// C++ program to illustrate for loop
  
#include 
using namespace std;
  
int main()
{
    int i = 0;
  
    // Writing a for loop
    // to print odd numbers upto N
    for (i = 1; i <= 10; i += 2) {
        cout << i << "\n";
    }
  
    return 0;
}


输出:
Hello World
Hello World
Hello World
Hello World
Hello World

空运行示例1:

1. Program starts.
2. i is initialized with value 1.
3. Condition is checked. 1 <= 5 yields true.
  3.a) "Hello World" gets printed 1st time.
  3.b) Updation is done. Now i = 2.
4. Condition is checked. 2 <= 5 yields true.
  4.a) "Hello World" gets printed 2nd time.
  4.b) Updation is done. Now i = 3.
5. Condition is checked. 3 <= 5 yields true.
  5.a) "Hello World" gets printed 3rd time
  5.b) Updation is done. Now i = 4.
6. Condition is checked. 4 <= 5 yields true.
  6.a) "Hello World" gets printed 4th time
  6.b) Updation is done. Now i = 5.
7. Condition is checked. 5 <= 5 yields true.
  7.a) "Hello World" gets printed 5th time
  7.b) Updation is done. Now i = 6.
8. Condition is checked. 6 <= 5 yields false.
9. Flow goes outside the loop to return 0

范例2:

C

// C program to illustrate for loop
  
#include 
  
int main()
{
    int i = 0;
  
    // Writing a for loop
    // to print odd numbers upto N
    for (i = 1; i <= 10; i += 2) {
        printf("%d\n", i);
    }
  
    return 0;
}

C++

// C++ program to illustrate for loop
  
#include 
using namespace std;
  
int main()
{
    int i = 0;
  
    // Writing a for loop
    // to print odd numbers upto N
    for (i = 1; i <= 10; i += 2) {
        cout << i << "\n";
    }
  
    return 0;
}
输出:
1
3
5
7
9

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