将 strcmp 与字符串数组一起使用
Using strcmp with string arrays
我正在制作一个测验程序，但我遇到了字符串数组和函数 strcmp 的问题
我想我可能不得不使用指针，但我不知道将哪个指针指定为指针
#include <iostream>
#include <cstring>
#include <stdio.h>
#include <string.h>
#include <cmath>
using namespace std;
int main(){
char question1[5][1000]={"Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: ",
"Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: ",
"Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:",
"Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: ",
"Question 5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "};
char answer1[5][2]={"A","C","B","A","D"};
char answer;
int score,i;
for(i=1;i<5;i++){
cout<<question1[i];
cin>>answer;
if(strcmp(answer,answer1[i])==0)
{
score++;
}
}
cout<<"Your score is "<<score;
}
answer 是 单个字符 而不是字符串。将它传递给需要字符串的函数时，不能将它用作字符串。对 strcmp 的调用应该会导致编译器对此发出警告。
直接比较字符，例如answer == answer1[i][0].
或者将类型改为字符串（最好是std::string，否则是char的数组）。
顺便提一下，您没有初始化变量 score。这意味着它的值将是 indeterminate 并且使用它（就像在 score++ 中一样）将导致 undefined behavior.
您需要显式初始化它：
int score = 0, i;
变量answer声明为单字节字符。
char answer;
不能存储字符串。
因此您不能将标准函数 strcmp 用于类型为 char 的对象。
你可以直接写
if ( answer == answer1[i][0] )
但最好将数组answer1声明为
const char answer1[] = { "ACBAD" };
或
const char *answer1 = { "ACBAD" };
并使用以下 if 语句
if ( answer == answer1[i] )
注意变量score没有初始化
int score,i;
你必须初始化它。而且循环中的索引应该从0开始。
int score = 0;
for( int i = 0;i < 5; i++ ){
//...
使用像 5 这样的幻数也是个坏主意。您可以引入一个命名常量。例如
const size_t N = 5;
char question1[N][1000] = { /*...*/ };
//...
for( size_t i = 0; i < N; i++ ){
//...
好吧，亲爱的OP，请允许我直言不讳。那不是 C++，那是带有 iostream 的 C 代码。此外，第一个问题从未打印出来，还发现了其他错误等。
None其中有一道题，如果你愿意学。 Here 是标准的 C++ 工作版本。请对照你的代码研究一下。
// clang++ prog.cc -Wall -Wextra -std=c++17
#include <iostream>
#include <array>
#include <string_view>
using namespace std;
// required for sv literal
using namespace std::literals;
// compile time std array of string literals
// each transformed to string_veiw's
// by using the `sv` std defined literal
constexpr array questions {
"Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: "sv,
"Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: "sv,
"Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:"sv,
"Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: "sv,
"Question #5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "sv
};
// same compile time structure as questions
// but for answers
constexpr array answers {"A"sv,"C"sv,"B"sv,"A"sv,"D"sv};
int main()
{
char answer {};
int score{} ;
// answer counter starts from 0
size_t j = 0;
// standard C++ 'sequence' loop
for ( auto & question : questions ) {
cout << question;
cin >> answer;
if( answer == answers.at[j][0] ) score++;
j++ ;
}
cout <<"Your score is "<< score;
return 42 ;
}
有人甚至可能会说标准 C++ 很简单，看看这个。一个人必须使用它。
附录
更好的设计是在单一结构上创建和操作，将答案和问题放在一起。一些横向思维总是有帮助的。
// clang++ prog.cc -Wall -Wextra -std=c++17
#include <iostream>
#include <array>
#include <string_view>
#include <utility> // std::pair
using namespace std;
using namespace std::literals;
constexpr std::array a_q_pairs {
pair{ 'A', "Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: "sv } ,
pair{ 'C', "Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: "sv},
pair{ 'B', "Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:"sv},
pair{ 'A', "Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: "sv},
pair{ 'D', "Question 5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "sv }
};
int main()
{
char user_answer {};
int score{} ;
// single loop
// requires no change on adding/removing answers/questions pairs
// no need to code index checking
for ( auto & a_and_q : a_q_pairs )
{
auto & answer = a_and_q.first ; // char
auto & question = a_and_q.second ; // string_view
cout << question ;
cin >> user_answer;
if( user_answer == answer ) score++;
}
cout <<"Your score is "<< score;
return 42 ;
}
精心设计的数据结构和在其上运行的简单算法。也许我会把那个 Niklaus Wirth book 擦掉？
必填项WandBox is here.
我正在制作一个测验程序，但我遇到了字符串数组和函数 strcmp 的问题
我想我可能不得不使用指针，但我不知道将哪个指针指定为指针
#include <iostream>
#include <cstring>
#include <stdio.h>
#include <string.h>
#include <cmath>
using namespace std;
int main(){
char question1[5][1000]={"Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: ",
"Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: ",
"Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:",
"Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: ",
"Question 5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "};
char answer1[5][2]={"A","C","B","A","D"};
char answer;
int score,i;
for(i=1;i<5;i++){
cout<<question1[i];
cin>>answer;
if(strcmp(answer,answer1[i])==0)
{
score++;
}
}
cout<<"Your score is "<<score;
}
answer 是 单个字符 而不是字符串。将它传递给需要字符串的函数时，不能将它用作字符串。对 strcmp 的调用应该会导致编译器对此发出警告。
直接比较字符，例如answer == answer1[i][0].
或者将类型改为字符串（最好是std::string，否则是char的数组）。
顺便提一下，您没有初始化变量 score。这意味着它的值将是 indeterminate 并且使用它（就像在 score++ 中一样）将导致 undefined behavior.
您需要显式初始化它：
int score = 0, i;
变量answer声明为单字节字符。
char answer;
不能存储字符串。
因此您不能将标准函数 strcmp 用于类型为 char 的对象。
你可以直接写
if ( answer == answer1[i][0] )
但最好将数组answer1声明为
const char answer1[] = { "ACBAD" };
或
const char *answer1 = { "ACBAD" };
并使用以下 if 语句
if ( answer == answer1[i] )
注意变量score没有初始化
int score,i;
你必须初始化它。而且循环中的索引应该从0开始。
int score = 0;
for( int i = 0;i < 5; i++ ){
//...
使用像 5 这样的幻数也是个坏主意。您可以引入一个命名常量。例如
const size_t N = 5;
char question1[N][1000] = { /*...*/ };
//...
for( size_t i = 0; i < N; i++ ){
//...
好吧，亲爱的OP，请允许我直言不讳。那不是 C++，那是带有 iostream 的 C 代码。此外，第一个问题从未打印出来，还发现了其他错误等。
None其中有一道题，如果你愿意学。 Here 是标准的 C++ 工作版本。请对照你的代码研究一下。
// clang++ prog.cc -Wall -Wextra -std=c++17
#include <iostream>
#include <array>
#include <string_view>
using namespace std;
// required for sv literal
using namespace std::literals;
// compile time std array of string literals
// each transformed to string_veiw's
// by using the `sv` std defined literal
constexpr array questions {
"Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: "sv,
"Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: "sv,
"Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:"sv,
"Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: "sv,
"Question #5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "sv
};
// same compile time structure as questions
// but for answers
constexpr array answers {"A"sv,"C"sv,"B"sv,"A"sv,"D"sv};
int main()
{
char answer {};
int score{} ;
// answer counter starts from 0
size_t j = 0;
// standard C++ 'sequence' loop
for ( auto & question : questions ) {
cout << question;
cin >> answer;
if( answer == answers.at[j][0] ) score++;
j++ ;
}
cout <<"Your score is "<< score;
return 42 ;
}
有人甚至可能会说标准 C++ 很简单，看看这个。一个人必须使用它。
附录
更好的设计是在单一结构上创建和操作，将答案和问题放在一起。一些横向思维总是有帮助的。
// clang++ prog.cc -Wall -Wextra -std=c++17
#include <iostream>
#include <array>
#include <string_view>
#include <utility> // std::pair
using namespace std;
using namespace std::literals;
constexpr std::array a_q_pairs {
pair{ 'A', "Question #1\n\nWhat is the formula for the area of a square?\n\nA.) Area = (Side)(Side)\nB.) Area = Side + Side\nC.) Area = Base + Height\nD.) Area = (pi)(Radius)(Radius)\nAnswer: "sv } ,
pair{ 'C', "Question #2\n\nWhat is the perimeter of a rectangle with length = 4 and width =8?\n\nA.) Perimeter = 4 + 8 = 12 units\nB.) Perimeter = (4)(8) = 32 units\nC.) Perimeter = 2(4) + 2(8) = 24 units\nD.) Perimeter = [2(4)][2(8)] = 128 units\nAnswer: "sv},
pair{ 'B', "Question #3\n\nWhat is the circumference of a Circle with Diameter = 10 units?\n\nA.) Circumference = (pi)(5)(5) = 78.5 units\nB.) Circumference = 2(pi)(5) = 31.41 units\nC.) Circumference = (pi)(10)(10) = 314 units\nD.) Circumference = 2(pi)(10) = 62.8 units\nAnswer:"sv},
pair{ 'A', "Question #4\n\nWhat is the measurement for the side of a square with Perimeter = 80?\n\nA.) 20 units\nB.) 80 units\nC.) 40 units\nD.) 50 units\nAnswer: "sv},
pair{ 'D', "Question 5\n\nWhat is the radius of a circle with area = 64pi square units?\n\nA.) 2pi units\nB.) 4pi units\nC.) 6pi units\nD.) 8pi units\nAnswer: "sv }
};
int main()
{
char user_answer {};
int score{} ;
// single loop
// requires no change on adding/removing answers/questions pairs
// no need to code index checking
for ( auto & a_and_q : a_q_pairs )
{
auto & answer = a_and_q.first ; // char
auto & question = a_and_q.second ; // string_view
cout << question ;
cin >> user_answer;
if( user_answer == answer ) score++;
}
cout <<"Your score is "<< score;
return 42 ;
}
精心设计的数据结构和在其上运行的简单算法。也许我会把那个 Niklaus Wirth book 擦掉？
必填项WandBox is here.