我是C ++的初学者,并且正在通过将学生的答案与答卷(“ 112341423114322314231231442314231223422”)进行比较,为学生的答案(“ 11 3 1133 22322314231432211231 34 2”)评分的课程。我必须比较学生答案的每个值,如果它们匹配,则加2分。如果不是,请减去1。现在,如果答案为空,那么我对学生的成绩没有任何帮助。
现在,代码如下:
//
#ifndef GRADER_H
#define GRADER_H
using namespace std;
#include <iostream>
class Grader {
protected:
int punt;
string answers, id, stans;
public:
Grader(){
answers = "112341423114322314231442314231223422";
int i;
char ans_arr[answers.length()];
for (i = 1; answers.length(); i++){
ans_arr[i] = answers[i];
}
}
Grader(string ans) {
answers = ans;
}
void Grade (string ans, string id, string stans) {
int punt = 0;
for (int i = 0; ans.length(); i++) {
if (stans[i] == ans[i]){
punt = punt + 2;
} else if ((stans[i] != ans[i]) && (stans[i] != ' ')) {
punt = punt - 1;
}
}
cout << punt;
}
};
#endif
//Main
#include <iostream>
#include "grader.h"
using namespace std;
int main() {
string ans = "112341423114322314231442314231223422";
Grader a(ans);
string student_id = "12345";
string student_ans = "11 3 1133 22322314231432211231 34 2";
int punt = 0;
a.Grade(ans,student_id,student_ans);
return 0;
}
这样,我遇到了段错误。我了解我正在处理我不应该处理的记忆,但是我不知道如何使这项工作有效。
答案 0 :(得分:3)
您的循环条件实际上不是条件。
来自w3schools:
for (statement 1; statement 2; statement 3) {
// code block to be executed
}
Statement 1 is executed (one time) before the execution of the code block.
Statement 2 defines the condition for executing the code block.
Statement 3 is executed (every time) after the code block has been executed.
例如,当您的条件为ans.length()
时,您的条件为i < ans.length()
。
由于ans.length()
将始终具有相同的(正)值,因此它将被解释为需要继续的循环,并且i
将继续增加。然后,类似ans[i]
的东西实际上正在尝试在数组末尾之后查看内存,如果未将越界内存分配给您的应用程序,则会导致段错误。
答案 1 :(得分:0)
ans.length
是36和stans.length is 35
。以下代码从stans
的外部读取。
for (int i = 0; ans.length(); i++) {
if (stans[i] == ans[i]){
这是内存访问错误:
Memory access error: reading from the outside of a memory block; abort execution.
# Reading 1 bytes from 0x9df62c0 will read undefined values.
#
# The memory-block-to-be-read (start:0x9df6290, size:48 bytes) is allocated at
# unknown_location (report this ::244)
#
# 0x9df6290 0x9df62bf
# +--------------------------+
# | memory-block-to-be-read |......
# +--------------------------+
# ^~~~~~~~~~
# the read starts at 0x9df62c0 that is right after the memory block end.
#
# Stack trace (most recent call first) of the read.
# [0] file:/prog.cc::28, 13
# [1] file:/prog.cc::50, 3
# [2] [libc-start-main]
以后您可以使用此link来调试代码的段错误。只需单击“开始”即可在终端中生成并运行您的代码。