C语言学习3-1：成绩检测，使用while和do...while得到九九乘法，1-1/2+1/3-1/4 .......+1/10求和，输入10进制打印2进制，求素数，猜随机产生的数字，16进制转二进制，

这个仅作为练习扩展使用，贴出代码，作为以后复习，不直接写结果。因为要自己推出

#include <stdio.h>

int main(void)
{
    int score;

    printf("pls input a score: ");
    scanf("%d", &score);

    if (score < 0 || score > 100)
    {
        printf("wrong. score from 0 to 100.
");    
    }
    else if (60 < score && score <= 100)
    {
        if (score < 70)    
        {
            printf("rank C!
");    
        }
        else if (70 <= score && score < 85)
        {
            printf("rank B!
");    
        }
        else
            printf("rank A!
");
    }
    else
    {
        if (score < 30)    
            printf("rank E!
");
        else
            printf("rank D!
");
    }

    return 0;
}

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    int i, j;

    i = 1;
    while (i <= 9)
    {
        j = 1;
        while (j <= i)
        {
            printf("%d x %d = %2d ", i, j, i * j);    
            j++;
        }

        i++;
        putchar('
');
    }
    printf("---------------------
");

    i = 1;
    do {
        j = 1;
        do {
            printf("%d x %d = %2d ", i, j, i * j);
            j++;    
        } while (j <= i);

        putchar('
');
        i++;
    } while (i <= 9);
    printf("---------------------
");

    i = 1;
labeli:

        j = 1;
    labelj:
        printf("%d x %d = %2d ", i, j, i * j);
        j++;
        if (j <= i)
            goto labelj;

    putchar('
');
    i++;
    if (i <= 9)
        goto labeli;
    
    return 0;
}

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    int i;
    double sum = 0;

    int flag = 1;
    
    for (i = 1; i <= 10; i++)
    {
        /*
         *if (i % 2 != 0)    
         *    sum += (double)1 / i;
         *else
         *    sum -= 1 / (double)i;
         */
        sum += flag * 1 / (double)i;
        flag *= -1;
    }

    printf("sum = %lf
", sum);

    return 0;
}

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    unsigned n;

    printf("pls input n: ");
    scanf("%d", &n);

    int i;
    for (i = 31; i >= 0; i--)
    {
        if (n & (1 << i))    
            putchar('1');
        else
            putchar('0');

        if (i % 4 == 0)
            putchar(' ');
    }
    putchar('
');

    return 0;
}

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    int num;
    int divider;
    int flag;
    int count = 0;

    for (num = 2; num <= 1000; num++)
    {
        flag = 0;
        for (divider = 2; divider <= num / 2; divider++)    
        {
            if (num % divider == 0)    
            {
                flag = 1;
                break;    
            }
        }

        if (!flag)
        {
            count++;
            printf("%d 是素数.
", num);
        }
    }

    printf("2 - 1000 一共有%d个素数.
", count);

    return 0;
}

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    int r;
    int guess;
    int ret;

    srand(time(NULL));
    r = rand() % 100;

    while (1)
    {
    retry:
        printf("input a num, to guess the password: ");    
        ret = scanf("%d", &guess);

        while (getchar() != '
')
            ;
        if (ret == 0)
        {
            printf("姿势不对, 重新输入.
");
            goto retry;
        }
    
        if (guess > r)
            printf("你输入的数大了.
");
        else if (guess < r)
            printf("你输入的数小了.
");
        else
        {
            printf("恭喜你, 中奖了.
");
            break;
        }
    }

    return 0;
}

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------

#include <stdio.h>

int main(void)
{
    char ch8 = '0', ch7 = '0', ch6 = '0', ch5 = '0',
         ch4 = '0', ch3 = '0', ch2 = '0', ch1 = '0';
    unsigned n;
    unsigned q, r;

    printf("pls input n: ");
    scanf("%u", &n);

    q = n;
    char ch;
    int cnt = 0;
    while (q > 0)
    {
        r = q % 16;
        q /= 16;

        if (r > 9)
            ch = (r - 10) + 'a';
        else
            ch = r + '0';

        switch (cnt)
        {
            case 0:
                ch1 = ch;
                break;
            case 1:
                ch2 = ch;
                break;
            case 2:
                ch3 = ch;
                break;
            case 3:
                ch4 = ch;
                break;
            case 4:
                ch5 = ch;
                break;
            case 5:
                ch6 = ch;
                break;
            case 6:
                ch7 = ch;
                break;
            case 7:
                ch8 = ch;
                break;
            default:    
                break;
        }

        cnt++;
    }

    printf("transformed: ");
    printf("0x%c%c%c%c %c%c%c%c
",
        ch8, ch7, ch6, ch5, ch4, ch3, ch2, ch1);

    return 0;
}

这个几个中就转换二进制有点意思，一个判断位为1还是0，一个一个的来共32次，转16进制就是不停的用除数除16得到每个阶段的余数，从低到高