C 語言自學經典 - 解答篇

開發環境

$ gcc --version
gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0

課後練習1

#include <stdio.h>

int main(int argc, const char *argv[]) {
    int year;
    
    scanf("%d", &year);
    if (year % 4 == 0 && year % 100 != 0) printf("yes\n");
    else if (year % 400 == 0) printf("yes\n");
    else printf("no\n");
    
    return 0;
}

課後練習2

#include <stdio.h>

int main(int argc, const char *argv[]) {
    int size;
    
    while (1) {
        scanf("%d", &size);
        if (size % 2 != 1) printf("not odd number!\n");
        else break;
    }
    
    int spaceCount = 0;
    while (size >= 1) {
        for (int i = 0; i <= spaceCount; i++) printf(" ");
        for (int i = 0; i < size; i++) printf("*");
        putchar('\n');
        size -= 2;
        spaceCount += 1;
    }
    
    return 0;
}

課後練習3

#include <stdio.h>

int main(int argc, const char *argv[]) {
    const int size = 10;
    int arr[size];
    
    for (int i = 0; i < size; i++) {
        scanf("%d", &arr[i]);
    }
    for (int i = 0; i < size; i++) {
        if (i % 2) printf("%d ", arr[i] / 2);
        else printf("%d ", arr[i] * 2);
    }
    putchar('\n');
    
    return 0;
}

課後練習4

#include <stdio.h>

int main(int argc, const char *argv[]) {
    char input[1010];
    char result[1010];
    int testcase;
    
    scanf("%d", &testcase);
    for (int t = 0; t < testcase; t++) {
        scanf("%s", input);
        
        int resultCounter = 0;
        int i = 0;
        while (input[i] != '\0') {
            if ((input[i] >= 65 && input[i] <= 90) ||
                (input[i] >= 97 && input[i] <= 122)) {
                result[resultCounter++] = input[i];
                }
            i += 1;
        }
        result[resultCounter] = '\0';
        printf("Test case %d: %s\n", t + 1, result);
    }
    return 0;
}

課後練習5

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

int arr[20][20];

void echo(int n) {
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < n; j++) {
            printf("%6d ", arr[i][j]);
        }
        putchar('\n');
    }
    return;
}

int main(int argc, const char *argv[]) {
    int n;
    int map[4][2] = {
        {0, 1}, {1, 0}, {0, -1}, {-1, 0}
    };
    memset(arr, 0, sizeof(int) * 20 * 20);
    
    scanf("%d", &n);
    if (n > 20) {
        printf("max size is 20. exit\n");
        return 0;
    }
    int mapCounter = 0;
    int rwalk = 0, cwalk = 0;
    int counter = 1;
    
    while (counter <= n * n) {
        while ( (rwalk >= 0 && rwalk <= n - 1) &&
                (cwalk >= 0 && cwalk <= n - 1) &&
                arr[rwalk][cwalk] == 0) {
            arr[rwalk][cwalk] = counter++;
            rwalk += map[mapCounter][0];
            cwalk += map[mapCounter][1];
        }
        
        rwalk -= map[mapCounter][0];
        cwalk -= map[mapCounter][1];
        mapCounter = (mapCounter + 1) % 4;
        rwalk += map[mapCounter][0];
        cwalk += map[mapCounter][1];
        
        if (rwalk < 0) rwalk = 0;
        if (rwalk >= n) rwalk = n - 1;
        if (cwalk < 0) cwalk = 0;
        if (cwalk >= n) cwalk = n - 1;
    }
    
    echo(n);
    
    return 0;
}

課後練習6

#include <stdio.h>

int main(int argc, const char *argv[]) {
    int num;
    
    scanf("%d", &num);
    printf("0x%08x\n", num);
    printf("0x%08x\n", num >> 16 | num << 16);
    
    return 0;
}

tags: clang