Checking if a String Contains a Number in C++
This article explores different methods for checking if a C++ string contains at least one numerical digit.
1. Using std::any_of with std::isdigit
This approach iterates through each character in the string and uses std::isdigit to check if it's a numerical digit. The std::any_of algorithm returns true if at least one character satisfies the condition.
#include
#include
#include
#include
bool containsNumber(const std::string& str) {
return std::any_of(str.begin(), str.end(), { return std::isdigit(c); });
}
int main() {
std::string str1 = "Hello123";
std::string str2 = "HelloWorld";
if (containsNumber(str1)) {
std::cout << "String 1 contains a number.\n";
} else {
std::cout << "String 1 does not contain a number.\n";
}
if (containsNumber(str2)) {
std::cout << "String 2 contains a number.\n";
} else {
std::cout << "String 2 does not contain a number.\n";
}
return 0;
}
2. Using a loop with std::isdigit
This approach iterates through the string using a loop and checks each character individually using std::isdigit. If a digit is found, the function returns true.
#include
#include
#include
bool containsNumber(const std::string& str) {
for (char c : str) {
if (std::isdigit(c)) {
return true;
}
}
return false;
}
int main() {
std::string str1 = "Hello123";
std::string str2 = "HelloWorld";
if (containsNumber(str1)) {
std::cout << "String 1 contains a number.\n";
} else {
std::cout << "String 1 does not contain a number.\n";
}
if (containsNumber(str2)) {
std::cout << "String 2 contains a number.\n";
} else {
std::cout << "String 2 does not contain a number.\n";
}
return 0;
}
3. Using regular expressions
This approach uses the std::regex class and a regular expression pattern to find a digit within the string.
#include
#include
#include
bool containsNumber(const std::string& str) {
std::regex pattern("[0-9]");
return std::regex_search(str, pattern);
}
int main() {
std::string str1 = "Hello123";
std::string str2 = "HelloWorld";
if (containsNumber(str1)) {
std::cout << "String 1 contains a number.\n";
} else {
std::cout << "String 1 does not contain a number.\n";
}
if (containsNumber(str2)) {
std::cout << "String 2 contains a number.\n";
} else {
std::cout << "String 2 does not contain a number.\n";
}
return 0;
}
Conclusion
These are just a few ways to check if a C++ string contains a number. The best approach depends on your specific needs and coding style. For simple checks, the loop with std::isdigit method is concise and efficient. For more complex pattern matching, regular expressions provide a powerful tool.