如何在文件中查找最小值/最大值答案

【问题标题】：how to find the min/max of values within a file如何在文件中查找最小值/最大值
【发布时间】：2017-06-09 22:25:48
【问题描述】：

#include <stdio.h>
int main(void)
{
    int num, i, total, average, min, max;
    min = num;
    max = num;
    FILE *ifile;
    ifile = fopen("scores.txt", "r");

    i = total = 0;
    while (fscanf(ifile, "%d", &num) != EOF) {
        i++;
        total += num;
    }

    printf("The total of the integers is %d.\n", total);
    printf("The number of integers in the file is %d.\n", i);

    average = total/i;

    printf("The average of the integers is %d.\n", average);

    while (fscanf(ifile, "%d", &num) != EOF) {
        if (num < min) {
            printf ("The minimum is %d\n", min);
        } else if (num > max) {
            printf ("The maximum is %d\n", max);
        }
    }

    fclose(ifile);
    return (0);
}

错误的代码部分是关于最小值/最大值的结尾。我不确定是否为此添加一个循环，甚至自己制作 min 和 max 变量。

【问题讨论】：

min = num; max = num; 这里，num 未初始化。在第一次迭代的任一循环中将min 和max 初始化为文件中的任何值，然后比较它们。
min = num;这行代码中num的值是多少？
我试图将文件中的 num 设为数字

标签： c max min

【解决方案1】：

您的最小/最大检测循环中至少存在三个问题：

首先，如chux所示，min和max没有被初始化；因此，在遍历数字时，声明 if (num < min)... 远不能保证正常工作（当然，max 也是如此）。所以用INT_MAX初始化min，用INT_MIN初始化max（都在<limits.h>中定义），这样已经在第一次迭代中min和max将被设置为文件中的值.

其次，检查if (num < min)... 会为您提供“本地”最小值，即到目前为止读取的所有数字的最小值，但不是“绝对”最小值，因为稍后可能会出现较小的数字。所以 min/max 将在循环结束时有效，而不是在迭代期间。

第三，if (num < min) ... else if (num > max) 至少在文件只包含一个数字时是错误的。

您的代码可能如下所示：

int min = INT_MAX;
int max = INT_MIN;
while (fscanf(ifile, "%d", &num) != EOF) {
    if (num < min)
        min = num;
    if (num > max)
        max = num;
}
// min/max are valid earliest at this point:
printf ("The minimum is %d\n", min);
printf ("The maximum is %d\n", max);

// Note that min/max will not be correct if the file does not contain any number;
// Note further, that fscanf(ifile, "%d", &num) != EOF may result in an endless loop if the file contains characters that "%d" will not read as a valid integral value.
// But this is left to the OP for further improvement :-)

【讨论】：

【解决方案2】：

考虑对您的代码进行以下修改：

#include <stdio.h>

int main(void) {
    int num, i, total, average, min, max;

    // open file
    FILE *ifile = fopen( "scores.txt", "r" );
    // if opening file fails, print error message and exit 1
    if (ifile == NULL) {
        perror("Error: Failed to open file.");
        return 1;
    }

    // initialize i and total to zero.
    i = total = 0;
    // read values from file until EOF is returned by fscanf,
    //   or until an error (hence the comparison "== 1")
    while(fscanf(ifile, "%d", &num) == 1) {
        // In first round of loop, initialize min and max
        //   to the number being read (num)
        // After min/max have been initialized, they can then
        //   be compared and modified in the second if statement 
        //   in the remaining loop rounds
        if (i == 0) {
            min = num;
            max = num;
            total += num;
            ++i;
            continue;
        } 
        if (num < min) {
            min = num;
        } else if (num > max) {
            max = num;
        }
        total += num;
        ++i;
    }

    // initialize average
    average = total/i;

    // summary
    printf("The sum of all integers in file is %d.\n", total);
    printf("The number of integers in file is %d.\n", i);
    printf("The average of all integers in file is %d.\n", average);
    printf ("The minimum is %d\n", min);
    printf ("The maximum is %d\n", max);

    fclose(ifile);
    return 0;
}

【讨论】：