极客笔记C++ 同时执行if和else语句
if-else语句被设计为计划A备用计划B。如果计划A失败，计划B就会被执行。我们如何使两个条件都起作用？我们在C和C++中解决这个鸡生蛋的问题的技巧是使用goto函数。goto函数将两个条件链接在一起，以便如果一个条件执行，后面的条件也同时执行。
C/C++语言中if-else语句的语法是
if (Boolean expression)
{
// The above written if condition will get executed only if
// the expression inside the Boolean is true
}
else
{
// The above written if condition will get executed only if
// the expression inside the Boolean of if the condition is false
}
C代码（if-else）
// Here we are writing down the C programming language code to demonstrate the
// concept of If statement along with its relevant code and output supported
// by syntax wherever necessary to explain the concept of executing both
// if and else statements simultaneously
#include
// The main driver code functionality starts from here
int main()
{
int j = 20;
if (j < 15) {
// printing the true condition of boolean
printf("j variable is smaller than 15");
}
else {
// printing the false condition of boolean
printf("j variable is greater than 15");
}
return 0;
// The main driver code functionality ends from here
输出:
j variable is greater than 15
C ++ 代码（if-else）
// Here we are writing down the C programming language code to demonstrate the
// concept of If statement along with its relevant code and output supported
// by syntax wherever necessary to explain the concept of executing both
// if and else statements simultaneously
#include
using namespace std;
// The main driver code functionality starts from here
int main()
{
int j = 20;
if (j < 15)
// printing the true condition of boolean
cout << "j variable is smaller than 15";
else
// printing the false condition of boolean
cout << "j variable is greater than 15";
return 0;
// The main driver code functionality ends from here
}
输出：
j variable is greater than 15
语法
if (condition1)
{
// The above written if condition will get executed only if
// the expression inside the condition1 is true
if (condition2)
{
// The above written if condition will get executed only if
// the expression inside the condition2 is true
}
}
嵌套if-else语句是特殊的条件语句；在这里，条件语句可以是互相独立的，或者嵌套在另一个条件语句内部。嵌套if-else语句可以与嵌套的for循环和嵌套的while循环进行比较。实现嵌套if-else语句在C和C++编程语言中进行讨论。
在C中的嵌套if-else语句
// Here we are writing down the C programming language code to demonstrate the
// concept of If statement along with its relevant code and output support
// by syntax wherever necessary to explain the concept of executing both
// if and else statements simultaneously
#include
// The main driver code functionality starts from here
int main()
{
int j = 10;
if (j == 10) {
if (j < 15)
printf("j is smaller than 15\n");
if (j < 12)
// printing the true condition of boolean
printf("j is smaller than 12 too\n");
else
// printing the condition of boolean if above is false
printf("j is greater than 15");
}
return 0;
// The main driver code functionality ends from here
}
输出：
j is smaller than 15
j is smaller than 12 too
在C++中的嵌套if-else
// Here we are writing down the C programming language code to demonstrate the
// concept of If statement along with its relevant code and output support
// by syntax wherever necessary to explain the concept of executing both
// if and else statements simultaneously
#include
using namespace std;
// The main driver code functionality starts from here
int main()
{
int j = 10;
if (j == 10) {
if (j < 15)
// printing the true condition of boolean
cout << "j is smaller than 15\n";
if (j < 12)
// printing the true condition of boolean
cout << "j is smaller than 12 too\n";
else
// printing the condition of boolean if above is false
cout << "j is greater than 15";
}
// The main driver code functionality ends from here
return 0;
}
输出:
j is smaller than 15
j is smaller than 12 too
以下我们将编写代码同时执行if和else语句。为了实现这个任务，我们将使用goto函数，并将它们标记为下一个目标条件语句。它可以是一个else语句，也可以是另一个if语句，即嵌套的if。
C 代码
#include
int main()
{
if (1)
{
label_1: printf("Hello ");
goto label_2;
}
else
{
goto label_1;
label_2: printf("JTP");
}
return 0;
}
输出：
Hello JTP
C++ 代码
#include
using namespace std;
int main()
{
if (1)
label_1: cout <<"Hello ";
goto label_2;
}
else
{
goto label_1;
label_2: cout <<"JTP";
}
return 0;
}
输出：
Hello JTP