您的代码中可能有一些错误。在这里，您将wordLen[ii]与未初始化且可能具有任何值的largestN进行比较。

int currentLvl, largestN, ii, iii, IV, V;

//Finds and stores the  largest number from the array into var:largestN.
for (ii = 0; ii < MAXLENGTH; ii++) {
    if (wordLen[ii] >= largestN)
        largestN = wordLen[ii];
}

如果largestN持有像641346这样的值，你试图用它创建一个数组：

int level[largestN];

顺便说一句，你可以有一个变量的多个循环。

//int i, ii, iii, IV, V;    // dont do this
int i;    // do this
for (i = 0; i < N; i++){
    // do something
}
for (i = 0; i < N; i++){    // use the same variable again
    // do something
}

请注意，第45行定义的largestN没有初始化，并且可以包含非常大的值。像Code：：blocks这样的IDE很可能会将所有变量归零，而gcc生成的更多优化编译则不会。因此，你可能会得到非常高的“酒吧”，基本上混乱了你的屏幕，使它很难看到什么是键入。
只需按以下方式更改第45行，这可能会给予您一些更合理的结果：

//Declaration of variables for Histogram.
int currentLvl, largestN = 0, ii, iii, IV, V;

另外，如果你已经在使用它，就不需要i，ii，iii等等，因为你在每次循环中都重置这个计数器，你可以在任何地方使用相同的变量'i'。此外，它不是标准的C语言，但所有现代编译器都允许你在for循环中定义一个变量，这更安全（注意for循环中的“int i”）：

for (int i = 0; i < MAXLENGTH; i++)
{
    // do something with i here. 
}

正如其他答案所说，您正在与未初始化的largestN进行比较，并调用undefined behavior。这里有另一个潜在的解决方案

// pretend that wordLen[0] is the largest value. Now, largestN
// is initialized
largestN = wordLen[0];
// loop, now starting at the 2nd index since we know
// largestN == wordLen[0]
for (i=1; i<MAXLENGTH; i++)
{
   // use > here instead of >=. If equal, largestN already contains that
   // value, no sense in overwriting it with the same value
   if (wordLen[i] > largestN)
        largestN = wordLen[i];
    }
}

在这里，您只处理正值，因此将largestN初始化为0就可以了，但一般来说，初始化为数组中已经存在的值是更健壮的方法。如果你的数组都是负数怎么办？那么0会大于所有这些，你不会得到一个准确的结果。

有几个问题..
1.有几个地方发生UB。
1.存储到wordLen时，nw可以超过MAXLENGTH
1.在您的示例输入文件中，有超过25个（即即MAXLENGTH）字。
1.我们需要检查一下是否有多余的。

1. largestN是 uninitialized，所以它可以有一个随机的[bad]值。
   1.后面的一些数组循环到MAXLENGTH。它们应该只循环到nw（有效元素的 * 实际 * 数量）。
   1.某些环路硬连接到25，而不是MAXLENGTH
2. level数组定义得太小。
   1.从原点1开始的索引超出数组的末尾，并使第一个元素保持为单位化。
   这里是[大部分]更正的代码。它是一个[大多数]错误和修复的注解。它可能在打印中仍然有一些错误，但它修复了大多数严重的错误：

#include <stdio.h>
#include <stdlib.h>

#ifndef MAXLENGTH
#define MAXLENGTH 25                    /* Maximum length of input. */
#endif

int
main()
{

    /* Histogram of length of words in its input. Vertical or Horizontal. (Vertical is hardest, so let's do that!). Identify words and count characters within each, store that length in a array that represents the length for each word. Draw based on the number of words, their lengths, and their maximum height (optional). */

    /* Identify when inside of a word, start counting. When leaving word, record c-count into array, reset count to 0 after. Until entering new word. */

    // Declaration of the Counter's variables here
    // The Histogram's variables are farther down below!
    int nw,
     c,
     cCount,
     wordLen[MAXLENGTH];
    int i = nw = cCount = 0;

    // Initialize wordLen into 0 to avoid garbage results from any potential unused members of the array.
#if 0
    for (i = 0; i < 25; i++) {
#else
    for (i = 0; i < MAXLENGTH; i++) {
#endif
        wordLen[i] = 0;
    }

    // Counts characters in each word and stores inside of chronological array.
    while ((c = getchar()) != EOF) {
        if (c == ' ' || c == '\t' || c == '\n') {
// NOTE/FIX: this can overflow wordLen causing UB (it scribbles on unrelated
// memory)
#if 1
            if (nw >= MAXLENGTH) {
                printf("overflow\n");
                exit(99);
            }
#endif
            wordLen[nw] = cCount;
            ++nw;
            cCount = 0;

        }
        else {
            ++cCount;
        }

    }
    // Prints first 4 words lengths for comparison purposes.
    printf("%d %d %d %d\n\n", wordLen[0], wordLen[1], wordLen[2], wordLen[3]);

    // Declaration of variables for Histogram.
    int currentLvl,
     largestN,
     ii,
     iii,
     IV,
     V;

    // Finds and stores the largest number from the array into var:largestN.
// NOTE/BUG: some elements may not have _actual_ values and largestN is
// _unitialized_
#if 0
    for (ii = 0; ii < MAXLENGTH; ii++) {
#else
    largestN = 0;
    for (ii = 0; ii < nw; ii++) {
#endif
        if (wordLen[ii] >= largestN)
            largestN = wordLen[ii];
    }

    // Declare and initialize array for comparison purposes for later use in the Histogram generation process.
// NOTE/BUG: this defines an array that is too short
#if 0
    int level[largestN];
#else
    int level[largestN + 1];
#endif

    level[0] = 0;
// NOTE/BUG: this goes one beyond the end of the valid data and it starts with
// an origin 1 array index
#if 0
    for (iii = 1; iii < largestN + 1; iii++) {
        level[iii] = iii;
    }
#else
    for (iii = 0; iii < largestN; iii++) {
        level[iii] = iii;
    }
#endif
    // printf("\n largest N is %d\n", largestN); //for testing
    // printf("wordLen 0 is: %d\n", wordLen[0]); //for testing

    /* Histogram generation: The logic is simple: From Top-left, move rightwards (in chronological order) and check which of the words' lengths reach the current level or height (starting from Top). Print a line at that spot if they ever do, print an empty space if they do not. Then move one step down, and repeat the process but comparing 1 level lower. Until bottom is reached. */
    // ss
// NOTE/BUG: this starts at one past the valid data
#if 0
    for (V = largestN; V > 0; V--) {
#else
    for (V = largestN - 1; V >= 0; V--) {
#endif
        currentLvl = level[V];

// NOTE/BUG: not sure which of these is correct
#if 1
        for (IV = 0; IV < MAXLENGTH; IV++) {
#else
        for (IV = 0; IV < nw; IV++) {
#endif
            if (wordLen[IV] >= currentLvl)
                printf("|");
            else {
                printf(" ");
            }
            printf(" ");
        }
        printf("\n");

    }

    return 0;
}

在上面的代码中，我使用了cpp条件来表示old与新代码：

#if 0
// old code
#else
// new code
#endif

#if 1
// new code
#endif

注意：这可以通过unifdef -k运行文件来清理。