c语言：长整数输入、长整数输出、加法、减法、除法、进制转换、退出系统

好的，我可以帮你实现这些功能。首先，需要了解长整数的表示方式。在C语言中，可以使用字符串来表示长整数，每一位数字都是一个字符，例如数字123456789可以表示为字符串"123456789"。下面是实现这些功能的代码示例：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX_SIZE 1000 // 定义最大长度

// 函数声明
void input(char* num);
void output(char* num);
void add(char* num1, char* num2, char* result);
void subtract(char* num1, char* num2, char* result);
void divide(char* num1, char* num2, char* result);
void convert(char* num, int from, int to);

int main() {
    char num1[MAX_SIZE], num2[MAX_SIZE], result[MAX_SIZE];
    int choice, from, to;
    
    while (1) {
        printf("请选择要进行的操作：\n");
        printf("1. 长整数输入\n");
        printf("2. 长整数输出\n");
        printf("3. 长整数加法\n");
        printf("4. 长整数减法\n");
        printf("5. 长整数除法\n");
        printf("6. 进制转换\n");
        printf("7. 退出系统\n");
        printf("请输入数字选择操作：");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                printf("请输入第一个长整数：");
                input(num1);
                printf("请输入第二个长整数：");
                input(num2);
                break;
            case 2:
                printf("第一个长整数为：");
                output(num1);
                printf("第二个长整数为：");
                output(num2);
                break;
            case 3:
                add(num1, num2, result);
                printf("两个长整数的和为：");
                output(result);
                break;
            case 4:
                subtract(num1, num2, result);
                printf("两个长整数的差为：");
                output(result);
                break;
            case 5:
                divide(num1, num2, result);
                printf("两个长整数的商为：");
                output(result);
                break;
            case 6:
                printf("请输入要转换的数字：");
                input(num1);
                printf("请输入要转换的进制（2-16）：");
                scanf("%d", &from);
                printf("请输入要转换成的进制（2-16）：");
                scanf("%d", &to);
                convert(num1, from, to);
                break;
            case 7:
                printf("已退出系统。\n");
                exit(0);
            default:
                printf("输入有误，请重新输入。\n");
                break;
        }
    }
    return 0;
}

// 长整数输入
void input(char* num) {
    scanf("%s", num);
}

// 长整数输出
void output(char* num) {
    printf("%s\n", num);
}

// 长整数加法
void add(char* num1, char* num2, char* result) {
    int carry = 0, len1 = strlen(num1), len2 = strlen(num2), len = 0, i, j, k;
    for (i = len1 - 1, j = len2 - 1; i >= 0 || j >= 0; i--, j--) {
        int a = i >= 0 ? num1[i] - '0' : 0;
        int b = j >= 0 ? num2[j] - '0' : 0;
        int sum = a + b + carry;
        result[len++] = sum % 10 + '0';
        carry = sum / 10;
    }
    if (carry) {
        result[len++] = carry + '0';
    }
    result[len] = '\0';
    for (i = 0, k = len - 1; i < k; i++, k--) {
        char temp = result[i];
        result[i] = result[k];
        result[k] = temp;
    }
}

// 长整数减法
void subtract(char* num1, char* num2, char* result) {
    int borrow = 0, len1 = strlen(num1), len2 = strlen(num2), len = 0, i, j, k;
    for (i = len1 - 1, j = len2 - 1; i >= 0 || j >= 0; i--, j--) {
        int a = i >= 0 ? num1[i] - '0' : 0;
        int b = j >= 0 ? num2[j] - '0' : 0;
        int diff = a - b - borrow;
        if (diff < 0) {
            diff += 10;
            borrow = 1;
        } else {
            borrow = 0;
        }
        result[len++] = diff + '0';
    }
    while (len > 1 && result[len - 1] == '0') {
        len--;
    }
    result[len] = '\0';
    for (i = 0, k = len - 1; i < k; i++, k--) {
        char temp = result[i];
        result[i] = result[k];
        result[k] = temp;
    }
}

// 长整数除法
void divide(char* num1, char* num2, char* result) {
    int len1 = strlen(num1), len2 = strlen(num2), i, j;
    char* dividend = (char*)malloc((len1 + 1) * sizeof(char));
    char* divisor = (char*)malloc((len2 + 1) * sizeof(char));
    char* quotient = (char*)malloc((len1 + 1) * sizeof(char));
    char* temp = (char*)malloc((len1 + 1) * sizeof(char));
    strcpy(dividend, num1);
    strcpy(divisor, num2);
    for (i = 0; i < len1 - len2; i++) {
        quotient[i] = '0';
    }
    quotient[i] = '\0';
    for (i = len1 - len2; i >= 0; i--) {
        int q = 0;
        while (strcmp(dividend, divisor) >= 0) {
            subtract(dividend, divisor, temp);
            strcpy(dividend, temp);
            q++;
        }
        quotient[i] = q + '0';
        for (j = strlen(dividend); j >= 1; j--) {
            dividend[j] = dividend[j - 1];
        }
        dividend[0] = '0';
    }
    while (strlen(quotient) > 1 && quotient[0] == '0') {
        strcpy(quotient, quotient + 1);
    }
    strcpy(result, quotient);
    free(dividend);
    free(divisor);
    free(quotient);
    free(temp);
}

// 进制转换
void convert(char* num, int from, int to) {
    char* table = "0123456789ABCDEF";
    char* result = (char*)malloc((strlen(num) * 4 + 1) * sizeof(char));
    char* temp = (char*)malloc((strlen(num) * 4 + 1) * sizeof(char));
    result[0] = '0';
    result[1] = '\0';
    while (strcmp(num, "0") > 0) {
        int r = 0, i;
        for (i = strlen(num) - 1; i >= 0; i--) {
            int d = num[i] - '0';
            r = r * from + d;
            num[i] = (r / to) + '0';
            r %= to;
        }
        temp[0] = table[r];
        temp[1] = '\0';
        strcat(temp, result);
        strcpy(result, temp);
    }
    printf("转换结果为：%s\n", result);
    free(result);
    free(temp);
}

注意，这里的加法、减法、除法都是针对正整数的，需要根据实际情况进行修改。另外，进制转换只支持2-16进制之间的转换。