程序中途停止，除非我按 ctrl+c，否则它不会终止

Question

这是我通过使用邻接矩阵来查找关系是否等价并计算等价类的代码

#include <stdio.h>
#include <string.h>
int mat[10][10], setln, relln, n, i, j;
char set[10], rel[50];
int checkrel(char);
int reflexive();
int symmetric();
int transitive();
int display();
int adjacency();
void main()
{
    int check = 1, r, s, t;
    printf("Enter the no. of elements in the set: ");
    scanf("%d", &n);
    gets(set);
    printf("Enter the elements of the set: ");
    fgets(set, 10, stdin);
    setln = strlen(set);
    while (check == 1)
    {
        printf("\nEnter the elements of relation in the manner '(a,b)(b,d)...':\n");
        fgets(rel, 50, stdin);
        relln = strlen(rel);
        if (relln < 5)
            continue;
        for (i = 0; i < relln - 5; i + 5)
        {

            if (rel[0] == '(' && (checkrel(rel[1])) && rel[2] == ',' && (checkrel(rel[3])) && rel[4] == ')')
                check = 0;
            else
            {
                printf("Enter a valid relation");
                break;
            }
        }
    }
    adjacency();
    r = reflexive();
    s = symmetric();
    t = transitive();
    if (r == 1)
        printf("\nThe relation is reflexive");
    else
        printf("\nThe relation is not reflexive");
    if (s == 1)
        printf("\nThe relation is symmetric");
    else
        printf("\nThe relation is not symmetric");
    if (t == 1)
        printf("\nThe relation is transitive");
    else
        printf("\nThe relation is not transitive");
    if (r == 1 && s == 1 && t == 1)
        printf("\nTherefore the relation is equivalent");
    else
        printf("\nTherefore the relation is not equivalent");
    int display();
    getchar();
}
int checkrel(char a)
{
    int m;
    for (int i = 0; i < setln; i++)
    {
        if (a == set[i])
            m = 1;
    }
    if (m == 1)
        return 1;
    else
        return 0;
}
int adjacency()
{
    int a, b;
    for (i = 1, j = 3; i < relln - 3; i + 5, j + 5)
    {
        for (int k = 0; k < setln; k++)
        {
            if (rel[i] == set[k])
                a = k;
        }
        for (int l = 0; l < setln; l++)
        {
            if (rel[j] == set[l])
                b = l;
        }
        mat[a][b] = 1;
    }
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (mat[i][j] != 1)
                mat[i][j] = 0;
        }
    }
}
int reflexive()
{
    for (i = 0; i < n; i++)
    {
        if (mat[i][i] != 1)
        {
            return 0;
        }
    }
    return 1;
}
int symmetric()
{
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (mat[i][j] != mat[j][i])
            {
                printf("\nThe relation is not equivalent as it is not symmetric");
                return 0;
            }
        }
    }
    return 1;
}
int transitive()
{
    int k;
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (mat[i][j] == 1)
            {
                for (k = 0; k < n; k++)
                {
                    if (mat[j][k] == 1 && mat[i][k] != 1)
                    {
                        printf("\nThe relation is not equivalent as it is not transitive");
                        return 0;
                    }
                }
            }
        }
    }
    return 1;
}
int display()
{
    printf("\nThe equivalence class is:\n{");
    for (i = 0; i < n; i++)
    {
        for (j = 0; j < n; j++)
        {
            if (mat[i][j] == 1)
                printf("(%c,%c)", set[i], set[j]);
        }
    }
    printf("}\n");
}

vscode 终端中的输出只是在此之后停止并且不会终止

Enter the no. of elements in the set: 3
Enter the elements of the set: 123

Enter the elements of relation in the manner '(a,b)(b,d)...':
(1,1)(2,2)
^C
D:\c>

光标只是固定在 (1,1)(2,2) 行之后的换行符中，直到我按 ctrl+c 我最后使用了 getchar() 但它不起作用

Answer 1

如果您在编译时启用警告（例如-Wall），编译器会标记您的问题：

orig.c:11:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
 void main()
      ^~~~
orig.c: In function ‘main’:
orig.c:16:2: warning: implicit declaration of function ‘gets’; did you mean ‘fgets’? [-Wimplicit-function-declaration]
  gets(set);
  ^~~~
  fgets
orig.c:27:34: warning: statement with no effect [-Wunused-value]
   for (i = 0;  i < relln - 5;  i + 5)
                                ~~^~~
orig.c: In function ‘adjacency’:
orig.c:78:43: warning: left-hand operand of comma expression has no effect [-Wunused-value]
  for (i = 1, j = 3;  i < relln - 3;  i + 5, j + 5)
                                           ^
orig.c:78:43: warning: statement with no effect [-Wunused-value]
orig.c:100:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
orig.c: In function ‘display’:
orig.c:161:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/tmp/ccIGyhw4.o: In function `main':
orig.c:(.text+0x45): warning: the `gets' function is dangerous and should not be used.

注意第 27 和 78 行的警告。

变化：

for (i = 0;  i < relln - 5;  i + 5)

进入：

for (i = 0;  i < relln - 5;  i += 5)

同样，改变：

for (i = 1, j = 3;  i < relln - 3;  i + 5, j + 5)

进入：

for (i = 1, j = 3;  i < relln - 3;  i += 5, j += 5)

在这两种情况下，您都有什么都不做的增量子句。所以，你有无限循环。

同时修复其他警告。而且，从不使用gets