墨尔本大学C语言期中考

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1. Ex7.04: Integer frequencies

1.1 Task

Write a program that reads as many as 1,000 integer values, and counts the frequency of each value in the input.

编写一个程序，读取多达 1000 个整数值，并计算输入中每个值的频率。

There are two quite different algorithms for this problem. Can you identify both of them? One of them imposes an upper limit on the input values so is less general than the other. Does it have any compensating advantages?

`arrayops.h` available

The arrayops.h library provides the functions read_int_array, int_swap, sort_int_array and print_int_array. You may use it if needed.

1.3 解析

学员代码

#include <stdio.h>

int main() {
    int input_number[1000];
    int input_frequence[1000] = {0};
    int count = 0;
    printf("Enter up to 1000 integer values, Ctrl+D to end:\n");
    while (scanf("%d", &input_number[count]) == 1) {
        count++;
    }
    for (int i = 0; i < count; i++) {
        input_frequence[input_number[i]]++;
        if (input_frequence[input_number[i]] != 0) {

            printf("%d\t%d\n", input_number[i], input_frequence[input_number[i]]);
        }
    }
}

main.c

#include <stdio.h>
#include "arrayops.h"  // 导入arrayops.h库，这个库提供了数组操作的函数。

int main(void) {
    int values[1000];  // 定义一个可以存放最多1000个整数的数组。
    int n, i, current, count;  // 定义变量：n用于存放实际读取的整数数量，i用于循环，current存放当前正在处理的整数，count存放current的频率。

    // 提示用户输入数据
//    printf("Enter as many as 1000 values, ^D to end\n");

    // 使用read_int_array函数读取输入的整数并存放到values数组中。
    // 返回值是实际读取的整数数量。
    n = read_int_array(values, 1000);
    // 输出实际读取的整数数量。
//    printf("%d values read into array\n", n);

    // 对读取的整数进行排序，这样相同的整数将位于数组中连续的位置。
    // 这使得计算每个整数的频率变得简单。
    sort_int_array(values, n);

    // 输出列标题。
    printf("Value   Freq\n");

    // 初始化i为0开始遍历数组。
    i = 0;
    while (i < n) {
        current = values[i];  // 记录当前正在处理的整数。
        count = 0;  // 初始化该整数的频率为0。

        // 如果数组中的当前整数与我们正在处理的整数相同，
        // 则增加频率计数并移动到数组的下一个位置。
        while (i < n && values[i] == current) {
            count++;
            i++;
        }

        // 输出当前整数及其频率。
        printf("%4d%7d\n", current, count);
    }

    return 0;  // 程序结束，返回0。
}

arrayops.c

/* array operations
 * Alistair Moffat, PPSAA, Chapter 7, December 2012
 * (c) University of Melbourne */
#include <stdio.h>

#include "arrayops.h"

/* ****
 * These functions are very slightly modified from insertionsort.c in Figure 7.4
 * Fig 7.4 on pg107 in PPSAA by Alistair Moffat, updating style and comments.
 * **** */

/* sorts n elements of array A in increasing order (2, 3, 4, 5)
 * using insertion sort (insertionsort.c, Figure 7.4 PPSAA) */
void
sort_int_array(int A[], int n) {
    /* assume that A[0] to A[n-1] have valid values */

    for (int i = 1; i < n; i++) {
        /* swap A[i] left into correct position (increasing order). */
        for (int j = i - 1; j >= 0 && A[j] > A[j + 1]; j--) {
            /* not there yet */
            int_swap(&A[j], &A[j + 1]);
        }
    }
}

/* exchange the values of the two variables indicated
 * by the arguments (insertionsort.c, Figure 7.4 PPSAA) */
void
int_swap(int *p1, int *p2) {
    int tmp = *p1;
    *p1 = *p2;
    *p2 = tmp;
}

/* read integers from input and store them in an array.
 * maxvals is the maximum number of elements that can be read in to the array,
 * all other values are discarded
 * returns the number of elements successfully read in
 * (insertionsort.c, Figure 7.4 PPSAA) */
int
read_int_array(int A[], int maxvals) {
    int n = 0, excess = 0, next;

    printf("Enter as many as %d values, ^D to end\n", maxvals);
    while (scanf("%d", &next) == 1) {
        if (n == maxvals) {
            excess += 1;
        } else {
            A[n] = next;
            n += 1;
        }
    }

    printf("%d values read into array", n);
    if (excess) {
        printf(", %d excess values discarded", excess);
    }
    printf("\n");
    return n;
}

/* print the elements of an array on one line
 * (insertionsort.c, Figure 7.4 PPSAA) */
void
print_int_array(int A[], int n) {
    for (int i = 0; i < n; i++) {
        printf(" %3d", A[i]);
    }
    printf("\n");
}

arrayops.h

/* arrayops.h: array operations
 * Alistair Moffat, PPSAA, Chapter 7, December 2012
 * (c) University of Melbourne */

/* read integers from input and store them in an array.
 * maxvals is the maximum number of elements that can be read in to the array,
 * all other values are discarded
 * returns the number of elements successfully read in
 * (insertionsort.c, Figure 7.4 PPSAA) */
int read_int_array(int A[], int n);

/* exchange the values of the two variables indicated
 * by the arguments (insertionsort.c, Figure 7.4 PPSAA) */
void int_swap(int *p1, int *p2);

/* sorts n elements of array A in increasing order (2, 3, 4, 5)
 * using insertion sort (insertionsort.c, Figure 7.4 PPSAA) */
void sort_int_array(int A[], int n);

/* print the elements of an array on one line
 * (insertionsort.c, Figure 7.4 PPSAA) */
void print_int_array(int A[], int n);

// see arrayops.c for implementation

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