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Program 1:

程序1：

#include <iostream>
using namespace std;
int main()
{
if (NULL) {
cout << "Hello World";
}
else {
cout << "Hii World";
}
return 0;
}

Output:

输出：

Hii World

Explanation:

说明：

The program will print "Hii World" on the console screen. Because the value of NULL is 0, then the if statement will be false and the else part will be executed.

该程序将在控制台屏幕上打印“ Hii World” 。 因为NULL的值为0 ，所以if语句将为false并将执行else部分。

Program 2:

程式2：

#include <iostream>
using namespace std;
int main()
{
int A = 5, B = 10, C = 20;
if (A && B > C) {
cout << "ABC";
}
else if (A = B || C == 20) {
cout << "PQR";
}
else {
cout << "XYZ";
}
return 0;
}

Output:

输出：

PQR

Explanation:

说明：

Execute the program step by step:

逐步执行程序：

    int A=5, B=10, C=20;
if(A&&B>C)
if(5&&10>20)
According to operator priority table, 
greater than (>) operator will evaluate 
before the logical and (&&) then
if(5&&0)
if(0)    
Then, program's execution will jump to,
else if(A=B || C==20)
According to the operator priority table, 
equal to (==) operator will be evaluated 
before the assignment and logical or operator
else if(10 || 20)
else if(1)
Here, condition is true and its block will be executed,
Then the final output will be "PQR".

Program 3:

程式3：

#include <iostream>
using namespace std;
int main()
{
int A = 15, B = 10, C = 20;
if (A > B) {
if (A >= 15) {
if (C > 10 ? A > 5 ? NULL : 1 : 2) {
cout << "111";
}
else {
cout << "222";
}
}
else {
cout << "333";
}
}
else {
cout << "444";
}
return 0;
}

Output:

输出：

222

Explanation:

说明：

Execute the program step by step:

逐步执行程序：

    int A=15, B=10, C=20;
if( A>B) that is if(15>10) condition is true then
if(A>=15) that is if(15>=15) condition is true then
Now checking,
if(C>10 ? A>5 ? NULL : 1 : 2) 
Here, 
C>10 that is 20>10 condition is true 
then check A>5 that is 15>5 condition is again true 
then it returns NULL, 
and the value of NULL is 0 and then if statement will be false. 
Then the else part will be executed 
and will print "222" on the console screen.

翻译自: https://www.includehelp.com/cpp-tutorial/conditional-statements-find-output-programs-set-1.aspx

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