C puzzles详解【51-57题】

第五十一题

Write a C function which does the addition of two integers without using the '+' operator. You can use only the bitwise operators.(Remember the good old method of implementing the full-adder circuit using the or, and, xor gates....)

题目讲解：

参考：
http://www.geeksforgeeks.org/add-two-numbers-without-using-arithmetic-operators/

int Add(int x, int y)

{

    // Iterate till there is no carry  

    while (y != 0)

    {

        // carry now contains common set bits of x and y

        int carry = x & y;  

 

        // Sum of bits of x and y where at least one of the bits is not set

        x = x ^ y; 

 

        // Carry is shifted by one so that adding it to x gives the required sum

        y = carry << 1;

    }

    return x;

}

或

int Add(int x, int y)

{

    if (y == 0)

        return x;

    else

        return Add( x ^ y, (x & y) << 1);

}

 

第五十二题

How do you print I can print % using the printf function? (Remember % is used as a format specifier!!!)

题目讲解：

参考：
http://www.geeksforgeeks.org/how-to-print-using-printf/

printf("%%");

printf("%c", '%');

printf("%s", "%");

第五十三题

What's the difference between the following two C statements? 

  const char *p;

  char* const p;

题目讲解：
const char *p:
p指向的值只读；
char* const p:
p的值只读；

第五十四题

What is the difference between memcpy and memmove?

题目讲解：
对重叠区域(overlapping regions)的处理有区别。

第五十五题

What is the format specifiers for printf to print double and float values?

题目讲解：
double: %lf
float: %f

第五十六题

Write a small C program to determine whether a machine's type is little-endian or big-endian.

题目讲解：
参考：
http://www.geeksforgeeks.org/little-and-big-endian-mystery/

unsigned int determine_endian()

{

unsigned int i = 1;

char *c = (char *)&i;

if (*c)

        return 0;//little endian

else

        return 1;//big endian

}

 

第五十七题

Write a C program which prints Hello World! without using a semicolon!!!

题目讲解：

#include <stdio.h>



int main()

{

while(printf(“Hello World!”)<0)

{}

}