如果将 print() 语句写入 if() 内，例如 if(print()) 会发生什么

如果将 print() 语句写在 if() 之类的 if(print()) 中会发生什么

先决条件： if-else

本文重点讨论在 if-else 条件语句中使用 print 语句时会发生什么。

例如：考虑下面的代码并预测输出。

C

// C program
 
#include 
 
// Driver code
int main()
{
    // if statement
    if (printf("I'm Awesome!\n"))
 
        // calling main() function
        main();
 
    // else-if statement
    else if (printf("I'm Not Awesome\n"))
 
        // calling main() function
        main();
}

C++

// C++ program
 
#include 
using namespace std;
 
// Driver code
int main()
{
    // if statement
    if (printf("I'm Awesome!\n"))
 
        // calling main() function
        main();
 
    // else-if statement
    else if (printf("I'm Not Awesome\n"))
 
        // calling main() function
        main();
    return 0;
}

Java

// Java program to implement the above approach
class GFG {
 
    public static void main(String[] args) {
 
        // if statement
        if (System.out.printf("I'm Awesome!\n") != null)
 
            // calling main() function
            main(null);
 
        // else-if statement
        else if (System.out.printf("I'm Not Awesome\n") != null)
 
            // calling main() function
            main(null);
    }
}
// This code contributed by Princi Singh

Python3

# Python program
# Driver code
# if statement
if(print("I'm Awesome!")):
     
   # calling main() function
   def main():
        
# else-if statement
elif(print("I'm Not Awesome")):
             
   # calling main() function
   def main():
 
# This code is contributed by shivanisinghss2110

C#

// C# program to implement the above approach
using System;
class GFG {
 
    public static void Main(String[] args) {
 
        // if statement
        if (Console.WriteLine("I'm Awesome!\n"))
 
            // calling Main() function
            Main(null);
 
        // else-if statement
        else if (Console.Write("I'm Not Awesome\n"))
 
            // calling Main() function
            Main(null);
    }
}
 
// This code is contributed by shivanisinghss2110

Javascript

// javascript program to implement the above approach  
function main() {
        // if statement
        if (document.write("I'm Awesome!\n"))
 
            // calling main() function
            main();
 
        // else-if statement
        else if (document.write("I'm Not Awesome\n"))
 
            // calling main() function
            main();
    }
    main();
 
 
// This code contributed by shikhasingrajput

猜测预期输出：对该程序输出的最普遍猜测是某种错误。

实际输出：但它的实际输出有点奇怪，而不是预期的输出。

解释：让我们讨论一下原因。

• 好像每次都满足条件并且由于 main()函数的递归调用，这个函数调用将理想地无限进行，但在实际场景中，一旦允许的函数调用堆栈被填满，它就会停止。
• 所以，首先，让我们了解为什么if条件中的打印函数没有给出错误以及它在内部是如何工作的。
• 这种行为基于一个简单的事实，即 C/C++ 等中的printf等打印函数返回一个整数值，该值等于它已成功打印的字符数。

让我们通过下面的程序来理解这一点——

C

// C program to implement
// the above approach
#include 
 
// Driver code
int main()
{
    // Nested printf function
    printf("%d", printf("GFG!\n"));
    return 0;
}

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Driver code
int main()
{
    // nested printf function
    printf("%d", printf("GFG!\n"));
    return 0;
}

Java

// Java program to implement
// the above approach
 
import java.util.*;
 
class GFG{
 
// Driver code
public static void main(String[] args)
{
    // nested printf function
    System.out.printf("%s", System.out.printf("GFG!\n"));
}
}
 
// This code is contributed by 29AjayKumar

蟒蛇3

# Python program to implement
# the above approach
 
# Nested printf function
print(print("GFG!\n"))
     
# This code is contributed by shivanisinghss2110

C＃

// C# program to implement
// the above approach
 
using System;
 
class GFG{
 
// Driver code
public static void Main(String[] args)
{
    // nested printf function
    Console.Write("GFG!\n");
}
}
  
 
// This code is contributed by shivanisinghss2110

Javascript

// JavaScript program to implement
// the above approach
 
// nested printf function
    document.write("GFG!\n");
 
 
// This code is contributed by shivanisinghss2110

输出

GFG!
5

说明：当遇到 printf 语句时，它转到外部printf函数并尝试打印其值，当程序尝试打印其值时，它遇到另一个printf并转到内部printf （如递归调用）以执行它然后它执行它并且内部printf函数返回5，因为该函数已成功打印 5 个字符（'G'、'F'、'G'、'!' 和 '\n'），因此返回一个整数值等于在这种情况下为 5。

如果总是返回true，是否会在内部使用print()？

从上面的例子，很容易理解printf函数在if语句中是如何工作的，以及条件是如何满足的。条件将始终满足，直到并且除非打印空字符串，如下面的代码所示 -

这个例子背后的唯一想法是演示如果printf函数返回“0”，那么if条件就会变成假。在所有其他情况下，字符串的长度是 1 还是 9999 都是正确的。

C

// C program to implement
// the above approach
#include 
 
// Driver code
int main()
{
    // printf function inside if statement
    if (printf(""))
 
        // printf function
        printf("Condition is True");
 
    // else statement
    else
 
        // printf function
        printf("Condition is False");
    return 0;
}

C++

// C++ program to implement
// the above approach
#include 
using namespace std;
 
// Driver code
int main()
{
    // printf function inside if statement
    if (printf(""))
 
        // printf function
        printf("Condition is True");
 
    // else statement
    else
 
        // printf function
        printf("Condition is False");
    return 0;
}

Java

// Java program to implement
// the above approach
import java.io.*;
 
class GFG
{
 
// Driver code
public static void main (String[] args)
{
   
    // printf function inside if statement
    if (System.out.print(""))
 
        // printf function
        System.out.print("Condition is True");
 
    // else statement
    else
 
        // printf function
        System.out.print("Condition is False");
}
}
 
// This code is contributed by shivanisinghss2110.

蟒蛇3

# Python program to implement
# the above approach
 
    # print function inside if statement
    if (print("")):
 
        # print function
        print("Condition is True")
 
    # else statement
    else:
 
        # print function
        print("Condition is False")
 
# This code is contributed by shivanisinghss2110.

C＃

// C# program to implement
// the above approach
using System;
 
class GFG
{
 
// Driver code
public static void Main (String[] args)
{
   
    // printf function inside if statement
    if (Console.Write(""))
 
        // printf function
        Console.Write("Condition is True");
 
    // else statement
    else
 
        // printf function
        Console.Write("Condition is False");
}
}
 
// This code is contributed by shivanisinghss2110

Javascript

// JavaScript program to implement
// the above approach
 
    // printf function inside if statement
    if (document.write(""))
 
        // printf function
        document.write("Condition is True");
 
    // else statement
    else
 
        // printf function
        document.write("Condition is False");
 
// This code is contributed by shivanisinghss2110.
 

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