用C语言新建main()函数，定义数组a1、a2，用a1存储字符串“hello”，用a2存储字符串“world”， 定义数组a3，思考如何将a1、a2内的字符串拼接，并赋值给a3，

在C语言中，你可以使用`strcat()`函数来拼接两个字符串，然后将其结果存储在一个新的字符数组中。这里是一个简单的示例，展示了如何创建`main()`函数并完成这个操作：

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

int main() {
    char a1[50] = "hello"; // 定义数组a1存储字符串
    char a2[50] = "world"; // 定义数组a2存储字符串

    // 检查a1是否有足够的空间来添加a2
    if (strlen(a1) + strlen(a2) + 1 <= sizeof(a1)) { // 加1是因为需要在拼接后添加终止符'\0'
        strcat(a1, a2); // 将a2拼接到a1
    } else {
        printf("a1的空间不足，无法拼接a2.\n");
        return 1;
    }

    char a3[100]; // 定义足够大的数组a3来存放拼接后的字符串
    strcpy(a3, a1); // 先复制a1到a3，因为strcat会改变a1的内容
    a3[strlen(a1)] = '\0'; // 添加终止符到a3

    printf("拼接后的字符串: %s\n", a3);

    return 0;
}

相关问题

用C语言写一个SHA-512加解密系统

SHA-512是一种安全哈希算法，用于产生消息摘要，不是加解密系统。下面是一个用C语言实现SHA-512算法的示例代码：

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

#define SHA512_BLOCK_SIZE 128
#define SHA512_DIGEST_SIZE 64

typedef struct SHA512_Context {
    uint64_t state[8];
    uint64_t bitcount[2];
    uint8_t buffer[SHA512_BLOCK_SIZE];
} SHA512_Context;

static const uint64_t K[80] = {
    0x428a2f98d728ae22ULL, 0x7137449123ef65cdULL,
    0xb5c0fbcfec4d3b2fULL, 0xe9b5dba58189dbbcULL,
    0x3956c25bf348b538ULL, 0x59f111f1b605d019ULL,
    0x923f82a4af194f9bULL, 0xab1c5ed5da6d8118ULL,
    0xd807aa98a3030242ULL, 0x12835b0145706fbeULL,
    0x243185be4ee4b28cULL, 0x550c7dc3d5ffb4e2ULL,
    0x72be5d74f27b896fULL, 0x80deb1fe3b1696b1ULL,
    0x9bdc06a725c71235ULL, 0xc19bf174cf692694ULL,
    0xe49b69c19ef14ad2ULL, 0xefbe4786384f25e3ULL,
    0x0fc19dc68b8cd5b5ULL, 0x240ca1cc77ac9c65ULL,
    0x2de92c6f592b0275ULL, 0x4a7484aa6ea6e483ULL,
    0x5cb0a9dcbd41fbd4ULL, 0x76f988da831153b5ULL,
    0x983e5152ee66dfabULL, 0xa831c66d2db43210ULL,
    0xb00327c898fb213fULL, 0xbf597fc7beef0ee4ULL,
    0xc6e00bf33da88fc2ULL, 0xd5a79147930aa725ULL,
    0x06ca6351e003826fULL, 0x142929670a0e6e70ULL,
    0x27b70a8546d22ffcULL, 0x2e1b21385c26c926ULL,
    0x4d2c6dfc5ac42aedULL, 0x53380d139d95b3dfULL,
    0x650a73548baf63deULL, 0x766a0abb3c77b2a8ULL,
    0x81c2c92e47edaee6ULL, 0x92722c851482353bULL,
    0xa2bfe8a14cf10364ULL, 0xa81a664bbc423001ULL,
    0xc24b8b70d0f89791ULL, 0xc76c51a30654be30ULL,
    0xd192e819d6ef5218ULL, 0xd69906245565a910ULL,
    0xf40e35855771202aULL, 0x106aa07032bbd1b8ULL,
    0x19a4c116b8d2d0c8ULL, 0x1e376c085141ab53ULL,
    0x2748774cdf8eeb99ULL, 0x34b0bcb5e19b48a8ULL,
    0x391c0cb3c5c95a63ULL, 0x4ed8aa4ae3418acbULL,
    0x5b9cca4f7763e373ULL, 0x682e6ff3d6b2b8a3ULL,
    0x748f82ee5defb2fcULL, 0x78a5636f43172f60ULL,
    0x84c87814a1f0ab72ULL, 0x8cc702081a6439ecULL,
    0x90befffa23631e28ULL, 0xa4506cebde82bde9ULL,
    0xbef9a3f7b2c67915ULL, 0xc67178f2e372532bULL,
    0xca273eceea26619cULL, 0xd186b8c721c0c207ULL,
    0xeada7dd6cde0eb1eULL, 0xf57d4f7fee6ed178ULL,
    0x06f067aa72176fbaULL, 0x0a637dc5a2c898a6ULL,
    0x113f9804bef90daeULL, 0x1b710b35131c471bULL,
    0x28db77f523047d84ULL, 0x32caab7b40c72493ULL,
    0x3c9ebe0a15c9bebcULL, 0x431d67c49c100d4cULL,
    0x4cc5d4becb3e42b6ULL, 0x597f299cfc657e2aULL,
    0x5fcb6fab3ad6faecULL, 0x6c44198c4a475817ULL
};

static const uint8_t padding[SHA512_BLOCK_SIZE] = {
    0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

static void SHA512_Transform(SHA512_Context *ctx) {
    uint64_t W[80];
    uint64_t A, B, C, D, E, F, G, H, T1, T2;
    int i;

    for (i = 0; i < 16; i++) {
        W[i] = ((uint64_t)ctx->buffer[i * 8 + 0] << 56) |
               ((uint64_t)ctx->buffer[i * 8 + 1] << 48) |
               ((uint64_t)ctx->buffer[i * 8 + 2] << 40) |
               ((uint64_t)ctx->buffer[i * 8 + 3] << 32) |
               ((uint64_t)ctx->buffer[i * 8 + 4] << 24) |
               ((uint64_t)ctx->buffer[i * 8 + 5] << 16) |
               ((uint64_t)ctx->buffer[i * 8 + 6] << 8) |
               ((uint64_t)ctx->buffer[i * 8 + 7] << 0);
    }

    for (i = 16; i < 80; i++) {
        W[i] = W[i-16] + W[i-7] + (ROTR(W[i-15], 1) ^ ROTR(W[i-15], 8) ^ (W[i-15] >> 7)) + (ROTR(W[i-2], 19) ^ ROTR(W[i-2], 61) ^ (W[i-2] >> 6));
    }

    A = ctx->state[0];
    B = ctx->state[1];
    C = ctx->state[2];
    D = ctx->state[3];
    E = ctx->state[4];
    F = ctx->state[5];
    G = ctx->state[6];
    H = ctx->state[7];

    for (i = 0; i < 80; i++) {
        T1 = H + (ROTR(E, 14) ^ ROTR(E, 18) ^ ROTR(E, 41)) + ((E & F) ^ (~E & G)) + K[i] + W[i];
        T2 = (ROTR(A, 28) ^ ROTR(A, 34) ^ ROTR(A, 39)) + ((A & B) ^ (A & C) ^ (B & C));
        H = G;
        G = F;
        F = E;
        E = D + T1;
        D = C;
        C = B;
        B = A;
        A = T1 + T2;
    }

    ctx->state[0] += A;
    ctx->state[1] += B;
    ctx->state[2] += C;
    ctx->state[3] += D;
    ctx->state[4] += E;
    ctx->state[5] += F;
    ctx->state[6] += G;
    ctx->state[7] += H;
}

void SHA512_Init(SHA512_Context *ctx) {
    memset(ctx, 0, sizeof(*ctx));
    ctx->state[0] = 0x6a09e667f3bcc908ULL;
    ctx->state[1] = 0xbb67ae8584caa73bULL;
    ctx->state[2] = 0x3c6ef372fe94f82bULL;
    ctx->state[3] = 0xa54ff53a5f1d36f1ULL;
    ctx->state[4] = 0x510e527fade682d1ULL;
    ctx->state[5] = 0x9b05688c2b3e6c1fULL;
    ctx->state[6] = 0x1f83d9abfb41bd6bULL;
    ctx->state[7] = 0x5be0cd19137e2179ULL;
}

void SHA512_Update(SHA512_Context *ctx, const uint8_t *data, size_t len) {
    size_t i;

    for (i = 0; i < len; i++) {
        ctx->buffer[ctx->bitcount[0] % SHA512_BLOCK_SIZE] = data[i];
        ctx->bitcount[0] += 8;
        if (ctx->bitcount[0] == 0) {
            ctx->bitcount[1]++;
        }
        if (ctx->bitcount[0] % SHA512_BLOCK_SIZE == 0) {
            SHA512_Transform(ctx);
        }
    }
}

void SHA512_Final(SHA512_Context *ctx, uint8_t *digest) {
    uint64_t totalbits = ctx->bitcount[0] + (ctx->bitcount[1] << 32);
    size_t padlen = SHA512_BLOCK_SIZE - (size_t)(ctx->bitcount[0] % SHA512_BLOCK_SIZE);
    int i;

    SHA512_Update(ctx, padding, padlen);
    SHA512_Update(ctx, (uint8_t *)&totalbits, sizeof(totalbits));

    for (i = 0; i < SHA512_DIGEST_SIZE / 8; i++) {
        digest[i * 8 + 0] = (ctx->state[i] >> 56) & 0xff;
        digest[i * 8 + 1] = (ctx->state[i] >> 48) & 0xff;
        digest[i * 8 + 2] = (ctx->state[i] >> 40) & 0xff;
        digest[i * 8 + 3] = (ctx->state[i] >> 32) & 0xff;
        digest[i * 8 + 4] = (ctx->state[i] >> 24) & 0xff;
        digest[i * 8 + 5] = (ctx->state[i] >> 16) & 0xff;
        digest[i * 8 + 6] = (ctx->state[i] >> 8) & 0xff;
        digest[i * 8 + 7] = (ctx->state[i] >> 0) & 0xff;
    }
}

int main() {
    SHA512_Context ctx;
    uint8_t digest[SHA512_DIGEST_SIZE];
    char message[] = "Hello, world!";
    size_t len = strlen(message);

    SHA512_Init(&ctx);
    SHA512_Update(&ctx, (uint8_t *)message, len);
    SHA512_Final(&ctx, digest);

    int i;
    for (i = 0; i < SHA512_DIGEST_SIZE; i++) {
        printf("%02x", digest[i]);
    }
    printf("\n");

    return 0;
}

该代码可以计算输入消息的SHA-512哈希值。要使用该代码，可以将要计算哈希值的消息存储在一个字符串中，然后调用`SHA512_Init`、`SHA512_Update`和`SHA512_Final`函数。最终的哈希值将存储在一个64字节的缓冲区中。