1.

/***将标准输入复制到标准输出，将所有大写字母转换为小写字母。*/#include 
     
      int main(void){        int ch;        while(ch = getchar() != EOF)        {            if (ch >= 'A' && ch <='Z')                ch = ch + 'a' - 'A';            putchar(ch);        }}
     

 

2.

/*从标准输入读取字符，并把它们写入到标准输出中，非字母字符按**输入形式输出，字母字符加密，加密为字母表上距其13个位置的字母。*/#include 
     
      int main(void){        int ch;        while(ch = getchar() != EOF)        {            if ((ch >= 'A' && ch <='M') ||                (ch >= 'a' && ch <= 'm'))                ch = ch + 13;            else if ((ch >= 'N' && ch <= 'Z') ||                     (ch >= 'n' && ch <= 'z'))                     ch = ch - 13;            putchar(ch);        }}
     

 

3

/*my code*/unsigned int reverse_bits (unsigned int value){    int a = 8 * sizeof (unsigned int);    unsigned int i, j = 1;    unsigned int new_value = 0;    for (; a > 0 ; a--)             /* 一开始条件脑残地写成a <= 0*/    {        new_value <<= 1;        new_value |= value & j;        value >>= 1;    }    return new_value;}/*guide's answer*/unsigned int reverse(unsigned int value){    unsigned int answer;    unsigned int i;    answer = 0;    for (i = 1; i != 0; i <<= 1)    {        answer <<= 1;        if (value & 1)            answer |= 1;        value >>= 1;    }    return answer;}int main (void){    unsigned int v = 0xfff;    printf("%x\n%x\n", reverse_bits(v),reverse(v));    return 0;}

 

4.

/***guide中，求数组index以及位数bits用了函数，这样的话的确方便了，**每次需要时调用即可，虽然这里不必这样，但当相同的表达式用到很多**时就需要了，其中的思想应该学习。*/#include 
     
             /*这两个头文件???啥用呢*/#include "bitarray.h"void set_bit(char bit_array[], unsigned bit_number){    unsigned int index, bits;    index = bit_number / 8;    bits  = bit_number % 8;    bit_array[index] |= (1 << bit_number);}void clear_bit(char bit_array[], unsigned bit_number){    unsigned int index, bits;    index = bit_number / 8;    bits  = bit_number % 8;    bit_array[index] &= ~(1 << bit_number);}/***guide中直接调用上面两个函数，简单多了好不好！o(╯□╰)o*/void assign_bit(char bit_array[], unsigned bit_number, int value){    unsigned int index, bits;    index = bit_number / 8;    bits  = bit_number % 8;    if (value)        bit_array[index] |= (1 << bit_number);    else        bit_array[index] &= ~(1 << bit_number);}int test_bit(char bit_array[], unsigned bit_number){     unsigned int index, bits;    index = bit_number / 8;    bits  = bit_number % 8;    bit_array[index] &= (1 << bit_number);    if (bit_array[index])        return 1;    else        return 0;}
     

 

5.

int store_bit_filed(int original_value,int value_to_store,    unsigned starting_bit, unsigned ending_bit){    /*step 1*/    unsigned int c = starting_bit - ending_bit + 1;    unsigned int mask = 1;    unsigned int i;    int new_value;    for (i = 1; i < c; i++)    {        mask |= (mask << 1);    }    mask <<= ending_bit - 1;    /*step 2*/    original_value = original_value & (~mask);    /*step 3此处课后的提示有误！！*/    value_to_store <<= ending_bit -1;    /*step 4*/    value_to_store &= mask;    return value_to_store;    /*step 5*/    new_value = value_to_store | original_value;    //return new_value;}#include 
     
      int main(void){    printf("%x\n", store_bit_filed(0xffff, 0x123, 13, 9));    return 0;}