C语言几道题

C语言刷题

1、打印1~100的质数

void Num(){    int i = 0, j = 0;    for (i = 1; i <= 100; ++i)    {        for (j = 2; j <= i; ++j)        {            if(i % j == 0)              {                break;            }        }        if (j == i)        {            printf("%d\n", i);        }    }}

2、实现类似atoi函数

void myatoi(){  char *str = "123456";                                                     int n = strlen(str);  int m;  int i = 0;  int sum = 0;  for (i = 0; i < strlen(str); ++i)  {    m = pow(10, --n);    sum += (str[i] - '0') * m;  }  printf("%d\n", sum); }

3、统计一个unsigned short类型的值中有多少位为1

void To2(){    unsigned short m = 85;    int a = m , b;    int num = 0;    while(1)    {        b = a % 2;        a = a / 2;        if (b == 1)        {            num++ ;        }        printf("%d %d\n", a, b);        if(a == 0)        {            break;        }    }    printf("%d\n", num);}

4、将unsigned int val中val的值取出每个字节并累加求和sum

unsigned int sum(unsigned int val){    char *m = (char *)&val;    printf("%x\n", m[0]+m[1]+m[2]+m[3]);}

5、测量机器大小端

//方法1：int HostOrder()//判断字节序{    int p = 0x1234;    char m = ((char *)&p)[0];    if (0x34 == m)    {        printf("小端\n");        return 0;//little    }    else    {        printf("大端\n");        return 1;//big    }}//方法2：union num {    int a;    char b;}test;int main(){    test.a = 0x123456;    if(test.b == 56)    {        printf("小端\n");    }    else    {        printf("大端\n");    }    return 1;}