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#include <stdio.h>
int main() {
    printf("\\  /\n");
    printf(" \\/\n");
    printf(" /\\\n");
    printf("/  \\\n");
    return 0;
}

2 学号

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#include<stdio.h>
int main () {
    char s[20];
    scanf("%s", s);
    printf("20%c%c", s[0], s[1]);
    return 0;
}

3 平均数

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#include <bits/stdc++.h>
using namespace std;

int main() {
    double a, b, c, d, n, z;
    cin >> a >> b >> c >> d;
    z = (a * 2.0 + b * 3.0 + c * 4.0 + d) / 10.0;
    cout << "Media: " << z << endl;
    if (z >= 7.0)
        cout << "Aluno aprovado." << endl;
    else if (z < 5.0)
        cout << "Aluno reprovado." << endl;
    else if (z < 7.0 && z >= 5.0) {
        cout << "Aluno em exame." << endl;
    }
}

4 质数

所有人必须掌握：

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#include <stdio.h>

int isPrime(int x) {
    for (int i = 2; i * i <= x; i++)
        if (x % i == 0)
            return 0;
    return x > 1;
}

int main() {
    int n;
    scanf("%d", &n);
    while(n--) {
        int x;
        scanf("%d", &x);
        if (isPrime(x)) {
            printf("%d is prime\n", x);
        } else {
            printf("%d is not prime\n", x);
        }
    }
    return 0;
}

有能力的可以学习这个：

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#include <stdio.h>
#define N 1000005
int isPrime[N + 1];

int main() {
    int n;
    scanf("%d", &n);
    for (int i = 0; i <= N; i++)
        isPrime[i] = 1;
    isPrime[0] = isPrime[1] = 0;
    for (int i = 2; i <= N; i++) {
        for (int j = 2 * i; j <= N; j += i)
            isPrime[j] = 0;
    }
    while(n--) {
        int x;
        scanf("%d", &x);
        if (isPrime[x]) {
            printf("%d is prime\n", x);
        } else {
            printf("%d is not prime\n", x);
        }
    }
    return 0;
}

5 斐波那契数列

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#include<stdio.h>

int main () {
    int a[100];
    a[1] = 1;
    a[2] = 1;
    int n;
    scanf("%d", &n);
    for (int i = 3; i <= n; i++)
        a[i] = a[i - 1] + a[i - 2];
    for (int i = 1; i <= n; i++)
        printf("%d ", a[i]);
    return 0;
}