C++ sample code for validating user input
This article introduces c++ to verify the legality of user input, which is used to detect and limit user input values. Including: 1. Restrict user input to be an integer (positive or negative integer); 2. Restrict user input to be a positive integer; 3. Restrict user input to be a positive number (may contain decimals); 4. Restrict user input to a number; 5. Restrict Can only be entered as English letters.
Tip : The following program requires the compiler to support the c++11 standard.
[If you use Dev-C++, you need to set: Open the "Tool [T]→Compile Options [C]" menu, add -std=c++11, and then press the "OK" button to take effect. See the red circle in the figure below:
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1. Limit user input to integers
It can be a positive or negative integer, and there are several source codes available for selection
Source code 1 :
#include <iostream>
using namespace std;
//判断输入的字符串是否为整数，直至合规才返归其值
int judge(int temp)
{
//对输入的合法性进行判断并返回有效的输入
//int temp;
cin.sync(); //清空输入流缓冲区
cin>>temp;
while(1)
{
if(cin.fail()||cin.bad()||cin.get()!='\n') //验证输入是否合法，其中cin.fail()和cin.bad()解决输入字符串和溢出的问题
cout<<"错误！请重新输入："<<endl; //cin.get()检查输入流中是否还有字符(如果有就表示输入的是形如123r或12.3的错误
else break; //输入合法则跳出循环
cin.clear(); //清空输入流缓冲区标志位，以免影响下次输入
cin.sync();
cin>>temp;
}
return temp;
}
int main()
{
cout<<"请输入整数："<<endl;
int a;
cout<<"合规的输入："<<judge(a)<<endl;
return 0;
}
The running effect is as follows:
Source code 2 :
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
//是整数返回1，否则返回0
bool isNumber3(const string& str)
{
return str.find_first_not_of( "-0123456789" ) == string::npos &&
str.front() != '.' && str.back() != '.';
}
int main(){
string str;
cout<<"请输入整数："<<endl;
cin>>str;
while(!isNumber3(str)){
cout<<"请输入整数，不要输入字母："<<endl;
cin>>str;
}
cout <<"合规输入："<<str<<endl;
//exit(EXIT_SUCCESS);
return 0;
}
The running effect is as follows:
2. Limit user input to positive integers
There are several source codes available for selection
source code 1
#include <iostream>
#include<string>
using namespace std;
//判断输入的字符串是否为正整数，若是，则合规返归其值 ，否则给出提示继续
int CheckNum(int& n)
{
int i;
string x; //用来接受输入
bool flag = false;
while (cin >> x) {
for (i = 0; i < x.size(); ++i) {
//判断是否为中文
if (x[i] & 0x80) {
cout << "\n输入错误，请重新输入正确的数字: ";
break;
}
//判断是否为字母或者其它字符
if (!isdigit(x[i])) {
cout << "\n输入错误，请重新输入正确的数字: ";
break;
}
}
if (i == x.size()) {
break; //如果字符串中所有字符都合法，则退出while循环
}
}
n = atoi(x.c_str()); //将string字符串转化为整数
return n;
}
int main()
{
int m,n;
while (true) {
cout << "请输入正整数:";
n=CheckNum(m);
cout <<"合规输入："<<n<<endl;
break; //退出循环
}
}
The running effect is as follows:
source code 2
#include<iostream>
#include<algorithm>
#include<cstring>
#include<stdlib.h> //为了使用 c_str() 函数
using namespace std;
//将string转为char数组并判断输入是否为正整数
int check1(string s){
char a[s.length()];
strcpy(a,s.c_str());
int i;
for(i = 0;i<s.length();i++){
//如果不是数字
if(!isdigit(a[i])){
return -1;
}
}
return 0;
}
//string 转 int
int s2i(string s)
{
return atoi( s.c_str() );
}
int main()
{
string n0;//判断用户输入用
int n;//真正存储的变量
cout<<"请输入："<<endl;
cin>>n0;
//判断输入的n0是否符合要求
while(check1(n0)){
cout<<"请输入正整数，不要输入负数或者小数或字母："<<endl;
cin>>n0;
}
n = s2i(n0);//string转为int存储
cout <<"合规输入："<<n<<endl;
}
The running effect is as follows:
Source code 3 :
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
//是正整数返回1，否则返回0
bool isNumber(const string& str)
{
return !str.empty() &&
find_if(str.begin(), str.end(),
[](unsigned char c) { return !isdigit(c); }) == str.end();
}
int main(){
string str;
cout<<"请输入正数："<<endl;
cin>>str;
while(!isNumber(str)){
cout<<"请输入正整数，不要输入负数或者小数或字母："<<endl;
cin>>str;
}
cout <<"合规输入："<<str<<endl;
//exit(EXIT_SUCCESS);
return 0;
}
The running effect is as follows:
3. Limit user input to positive numbers
can contain decimals
Source code 1 :
#include<iostream>
#include<algorithm>
#include<cstring>
#include<stdlib.h> //为了使用 c_str() 函数
using namespace std;
//将string转为char数组并判断输入是否为正数
int check2(string s){
char a[s.length()];
strcpy(a,s.c_str());
int i;
for(i = 0;i<s.length();i++){
//如果不是数字且不是小数点
if((!isdigit(a[i])) && (a[i]!='.')){
return -1;
}
}
return 0;
}
//string 转 double
double s2d(string s)
{
return atof( s.c_str() );
}
int main(){
string n0;//判断用户输入用
double n;//真正存储的变量
cout<<"请输入正数："<<endl;
cin>>n0;
//判断输入的n0是否符合要求
while(check2(n0)){
cout<<"请输入正数，不要输入负数或字母："<<endl;
cin>>n0;
}
n = s2d(n0);//string转为double存储
cout <<"合规输入："<<n<<endl;
}
The running effect is as follows:
Source code 2 :
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
//是正数返回1，否则返回0
bool isNumber3(const string& str)
{
return str.find_first_not_of( ".0123456789" ) == string::npos &&
str.front() != '.' && str.back() != '.';
}
int main(){
string str;
cout<<"请输入正数："<<endl;
cin>>str;
while(!isNumber3(str)){
cout<<"请输入正数，不要输入负数或字母："<<endl;
cin>>str;
}
cout <<"合规输入："<<str<<endl;
return 0;
}
The running effect is as follows:
4. Limit user input to a number
Include positive and negative integers, positive and negative decimals, but cannot contain letters
The source code is as follows
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
//是数返回1，否则返回0
bool isNumber3(const string& str)
{
return str.find_first_not_of( "+-.0123456789" ) == string::npos &&
str.front() != '.' && str.back() != '.';
}
int main(){
string str;
cout<<"请输入数："<<endl;
cin>>str;
while(!isNumber3(str)){
cout<<"请输入数，不要输入字母："<<endl;
cin>>str;
}
cout <<"合规输入："<<str<<endl;
//exit(EXIT_SUCCESS);
return 0;
}
The running effect is as follows:
5. Only English letters can be input
The source code is as follows
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
//是英语字母返回1，否则返回0
bool isNumber3(const string& str)
{
return str.find_first_not_of( "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz" ) == string::npos &&
str.front() != '.' && str.back() != '.';
}
int main(){
string str;
cout<<"请输入英语字母："<<endl;
cin>>str;
while(!isNumber3(str)){
cout<<"请输英语字母："<<endl;
cin>>str;
}
cout <<"合规输入："<<str<<endl;
//exit(EXIT_SUCCESS);
return 0;
}The running effect is as follows:
OK!