我整理了10个非常基础的c语言循环结构和选择结构的小题目，看看你的基础够不够牢固。

#include<stdio.h>
#include<time.h>
#include<stdlib.h>
int main()
{
int i, x, max, min;
//srand((unsigned)time(NULL));
srand(time(0));//随机因子
x = rand() % 90;
min = max = x;
printf("%d,", x);
for (i = 1; i <= 9; i++)
{
    x = rand() % 90;
    printf("%d,", x);
    if (max < x) max = x;
    if (min > x) min = x;
}
printf("\nmax=%d\n", max);
printf("min=%d\n", min);
return 0;
}

#include <stdio.h>
#include <math.h>
void main()
{
    int i, n;
    scanf_s("%d", &amp;n);
    for (i = 2; i < n; i++) {
        if (n % i == 0) {
            printf("%d不是素数", n);
            return;
        }
        if (n % i != 0) {
            printf("%d是素数", n);
            return;
        }
    }
}

#include <stdio.h>
#include <math.h>
void main()
{
    int i, j=0, n,sum=0;
    //scanf_s("%d", &amp;n);
    for (i = 100; i <= 500; i++) {
        n = sqrt(i);
        for (j = 2; j <= n; j++) {
            if (i % j == 0) {
                break;
            }
        }
        if (j >= n + 1) {
            printf("%d\t", i);
            sum++;
        }
        
    }
    printf("\n一共%d个", sum);
}

#include<stdio.h>
int main()
{
    int i,j,s;
    for(i=1;i<=1000;i++)
    {
        s=0;
        for(j=1;j<i;j++)
            if(i%j==0)
                s=s+j;
        if(s==i)
            printf("%d\n",i);
    }	
} 

#include<stdio.h>
int main()
{
    long i,m,n,x,t;
    scanf_s("%ld%ld", &amp;m, &amp;n);

    for (i=m;i<=n; i++)
    {
        if (i % 3 == 0) { //判断是否能被3整除
            x = i;
            while (x > 0) {//循环看看有没有除以10余数为5的，有的话输出
                t = x % 10;
                if (t == 5) {
                    printf("%ld\n", i);
                    break;
                }
                x = x / 10;
            }
        }
    }
}

#include <stdio.h>
int main()
{
    int f1 = 1, f2 = 1, f3;
    int i;
    printf("%d\n%d\n", f1, f2);
    for (i = 3; i <= 40; i++)
    {
        f3 = f1 + f2;//先写f3=f1+f2然后输出f3，之后再给f1和f2赋值
        printf("%d\n", f3);
        f1 = f2;
        f2 = f3;
    }
}

#include <stdio.h>
int main()
{
    char s;
    int z, k, n, q;
    z = k = n = q = 0;
    s = getchar();//从控制台接收输入，遇到回车结束，我们while判断就用回车来判断
    while (s != '\n') { //对于不确定的循环用while
        if (s >= 'a' &amp;&amp; s <= 'z' || s >= 'A' &amp;&amp; s <= 'Z')
            z++;
        else if (s == ' ')
            k++;
        else if (s >= '0' &amp;&amp; s <= '9')
            n++;
        else q++;
        s = getchar();
    }
    printf("字母:%d\n空格:%d\n数字:%d\n其它:%d\n", z, k, n, q);

}

#include<stdio.h>
void main()
{
    char c;
    c = getchar();
    while (c != '\n')
    {
        if (c == 'b')
        {
                    c = c + 1 - 32;//这里重要的就是ASCII码，转化为大写是+十进制32
        }
        printf("%c", c);
        c = getchar();
    }
}

#include<stdio.h>
void main()
{
    int i, j, k;
    for (i = 1; i < 10; i++)
    {
        for (j = 10; j > i; j--)
            printf(" ");//输出空格，倒叙
        for (k = 1; k <= i; k++)
            printf("%d", k);//输出数字1++
        for (k = i; k > 1; k--)
            printf("%d", k-1);//倒叙输出--
        printf("\n");
    }
}

#include<stdio.h>
void main()
{
    int p, r, a, b, temp;
    printf("请输入两个正整数：");
    scanf_s("%d,%d", &amp;a, &amp;b);
    if (b < a)
    {
        temp = b;
        b = a;
        a = temp;
    }
    p = b * a;
    while (a != 0)
    {
        r = b % a;
        b = a;
        a = r;
    }
    printf("它们的最大公约数为：%d\n", b);
    printf("它们的最小公倍数为：%d\n", p / b);
}