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: %lffloat: %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)
{}
}