请用C语言编写一段完整代码，用户可以先选择进入功能一还是功能二，功能一是计算输入的分子式的相对分子质量，功能二是查询输入的元素（1-36号元素且不区分大小写）的相对原子质量

好的，以下是代码实现：

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

/* 计算相对分子质量 */
float calculate_molecular_weight(char formula[]) {
    float total_weight = 0.0f;
    int len = strlen(formula);
    int i = 0;

    while (i < len) {
        int j = i + 1;
        char current_elem = formula[i];

        /* 处理元素符号后面的数字 */
        while (j < len && isdigit(formula[j])) {
            j++;
        }
        int num = 1;
        if (j > i + 1) {
            num = atoi(formula + i + 1);
        }

        /* 根据元素符号计算相对原子质量 */
        if (current_elem == 'H') {
            total_weight += 1.008f * num;
        } else if (current_elem == 'C') {
            total_weight += 12.011f * num;
        } else if (current_elem == 'O') {
            total_weight += 15.999f * num;
        } else if (current_elem == 'N') {
            total_weight += 14.007f * num;
        } else {
            printf("无法识别的元素符号：%c\n", current_elem);
            return -1.0f;
        }

        i = j;
    }

    return total_weight;
}

/* 查询相对原子质量 */
float query_atomic_weight(char symbol[]) {
    int atomic_number = -1;
    float atomic_weight = -1.0f;

    /* 根据元素符号查询原子序数 */
    if (strcmp(symbol, "H") == 0 || strcmp(symbol, "h") == 0) {
        atomic_number = 1;
    } else if (strcmp(symbol, "He") == 0 || strcmp(symbol, "he") == 0) {
        atomic_number = 2;
    } else if (strcmp(symbol, "Li") == 0 || strcmp(symbol, "li") == 0) {
        atomic_number = 3;
    } else if (strcmp(symbol, "Be") == 0 || strcmp(symbol, "be") == 0) {
        atomic_number = 4;
    } else if (strcmp(symbol, "B") == 0 || strcmp(symbol, "b") == 0) {
        atomic_number = 5;
    } else if (strcmp(symbol, "C") == 0 || strcmp(symbol, "c") == 0) {
        atomic_number = 6;
    } else if (strcmp(symbol, "N") == 0 || strcmp(symbol, "n") == 0) {
        atomic_number = 7;
    } else if (strcmp(symbol, "O") == 0 || strcmp(symbol, "o") == 0) {
        atomic_number = 8;
    } else if (strcmp(symbol, "F") == 0 || strcmp(symbol, "f") == 0) {
        atomic_number = 9;
    } else if (strcmp(symbol, "Ne") == 0 || strcmp(symbol, "ne") == 0) {
        atomic_number = 10;
    } else if (strcmp(symbol, "Na") == 0 || strcmp(symbol, "na") == 0) {
        atomic_number = 11;
    } else if (strcmp(symbol, "Mg") == 0 || strcmp(symbol, "mg") == 0) {
        atomic_number = 12;
    } else if (strcmp(symbol, "Al") == 0 || strcmp(symbol, "al") == 0) {
        atomic_number = 13;
    } else if (strcmp(symbol, "Si") == 0 || strcmp(symbol, "si") == 0) {
        atomic_number = 14;
    } else if (strcmp(symbol, "P") == 0 || strcmp(symbol, "p") == 0) {
        atomic_number = 15;
    } else if (strcmp(symbol, "S") == 0 || strcmp(symbol, "s") == 0) {
        atomic_number = 16;
    } else if (strcmp(symbol, "Cl") == 0 || strcmp(symbol, "cl") == 0) {
        atomic_number = 17;
    } else if (strcmp(symbol, "Ar") == 0 || strcmp(symbol, "ar") == 0) {
        atomic_number = 18;
    } else if (strcmp(symbol, "K") == 0 || strcmp(symbol, "k") == 0) {
        atomic_number = 19;
    } else if (strcmp(symbol, "Ca") == 0 || strcmp(symbol, "ca") == 0) {
        atomic_number = 20;
    } else if (strcmp(symbol, "Sc") == 0 || strcmp(symbol, "sc") == 0) {
        atomic_number = 21;
    } else if (strcmp(symbol, "Ti") == 0 || strcmp(symbol, "ti") == 0) {
        atomic_number = 22;
    } else if (strcmp(symbol, "V") == 0 || strcmp(symbol, "v") == 0) {
        atomic_number = 23;
    } else if (strcmp(symbol, "Cr") == 0 || strcmp(symbol, "cr") == 0) {
        atomic_number = 24;
    } else if (strcmp(symbol, "Mn") == 0 || strcmp(symbol, "mn") == 0) {
        atomic_number = 25;
    } else if (strcmp(symbol, "Fe") == 0 || strcmp(symbol, "fe") == 0) {
        atomic_number = 26;
    } else if (strcmp(symbol, "Co") == 0 || strcmp(symbol, "co") == 0) {
        atomic_number = 27;
    } else if (strcmp(symbol, "Ni") == 0 || strcmp(symbol, "ni") == 0) {
        atomic_number = 28;
    } else if (strcmp(symbol, "Cu") == 0 || strcmp(symbol, "cu") == 0) {
        atomic_number = 29;
    } else if (strcmp(symbol, "Zn") == 0 || strcmp(symbol, "zn") == 0) {
        atomic_number = 30;
    } else if (strcmp(symbol, "Ga") == 0 || strcmp(symbol, "ga") == 0) {
        atomic_number = 31;
    } else if (strcmp(symbol, "Ge") == 0 || strcmp(symbol, "ge") == 0) {
        atomic_number = 32;
    } else if (strcmp(symbol, "As") == 0 || strcmp(symbol, "as") == 0) {
        atomic_number = 33;
    } else if (strcmp(symbol, "Se") == 0 || strcmp(symbol, "se") == 0) {
        atomic_number = 34;
    } else if (strcmp(symbol, "Br") == 0 || strcmp(symbol, "br") == 0) {
        atomic_number = 35;
    } else if (strcmp(symbol, "Kr") == 0 || strcmp(symbol, "kr") == 0) {
        atomic_number = 36;
    }

    /* 根据原子序数查询相对原子质量 */
    switch (atomic_number) {
        case 1:
            atomic_weight = 1.008f;
            break;
        case 2:
            atomic_weight = 4.003f;
            break;
        case 3:
            atomic_weight = 6.941f;
            break;
        case 4:
            atomic_weight = 9.012f;
            break;
        case 5:
            atomic_weight = 10.811f;
            break;
        case 6:
            atomic_weight = 12.011f;
            break;
        case 7:
            atomic_weight = 14.007f;
            break;
        case 8:
            atomic_weight = 15.999f;
            break;
        case 9:
            atomic_weight = 18.998f;
            break;
        case 10:
            atomic_weight = 20.180f;
            break;
        case 11:
            atomic_weight = 22.990f;
            break;
        case 12:
            atomic_weight = 24.305f;
            break;
        case 13:
            atomic_weight = 26.982f;
            break;
        case 14:
            atomic_weight = 28.086f;
            break;
        case 15:
            atomic_weight = 30.974f;
            break;
        case 16:
            atomic_weight = 32.066f;
            break;
        case 17:
            atomic_weight = 35.453f;
            break;
        case 18:
            atomic_weight = 39.948f;
            break;
        case 19:
            atomic_weight = 39.098f;
            break;
        case 20:
            atomic_weight = 40.078f;
            break;
        case 21:
            atomic_weight = 44.956f;
            break;
        case 22:
            atomic_weight = 47.867f;
            break;
        case 23:
            atomic_weight = 50.942f;
            break;
        case 24:
            atomic_weight = 52.000f;
            break;
        case 25:
            atomic_weight = 54.938f;
            break;
        case 26:
            atomic_weight = 55.845f;
            break;
        case 27:
            atomic_weight = 58.933f;
            break;
        case 28:
            atomic_weight = 58.693f;
            break;
        case 29:
            atomic_weight = 63.546f;
            break;
        case 30:
            atomic_weight = 65.390f;
            break;
        case 31:
            atomic_weight = 69.723f;
            break;
        case 32:
            atomic_weight = 72.630f;
            break;
        case 33:
            atomic_weight = 74.922f;
            break;
        case 34:
            atomic_weight = 78.960f;
            break;
        case 35:
            atomic_weight = 79.904f;
            break;
        case 36:
            atomic_weight = 83.798f;
            break;
        default:
            printf("无法识别的元素符号：%s\n", symbol);
            atomic_weight = -1.0f;
            break;
    }

    return atomic_weight;
}

int main() {
    int choice = 0;
    char input[100];
    float result = 0.0f;

    /* 选择功能 */
    printf("请选择功能：\n");
    printf("1. 计算分子式的相对分子质量\n");
    printf("2. 查询元素的相对原子质量\n");
    scanf("%d", &choice);

    switch (choice) {
        case 1:
            printf("请输入分子式：\n");
            scanf("%s", input);
            result = calculate_molecular_weight(input);
            if (result >= 0.0f) {
                printf("相对分子质量为：%.3f\n", result);
            }
            break;
        case 2:
            printf("请输入元素符号：\n");
            scanf("%s", input);
            result = query_atomic_weight(input);
            if (result >= 0.0f) {
                printf("相对原子质量为：%.3f\n", result);
            }
            break;
        default:
            printf("无效的选择！\n");
            break;
    }

    return 0;
}

注意事项：

- 代码中使用了 `isdigit` 函数来判断字符是否为数字。
- 代码中使用了 `strcmp` 函数来比较字符串是否相等。
- 代码中使用了 `switch` 语句来根据原子序数查询相对原子质量。
- 代码中使用了 `atoi` 函数来将字符串转换为整数。