Date helpers
- C++ course
- Intermediate
- Lesson 22/116
- 6 min
Add date processing functions.
Date helpers
Our third helper is a date formatter: formatDate. This method takes year, month and day values and returns a string in YYYY-MM-DD format. This ISO 8601 format is common in data exchange.
Example: static std::string formatDate(int year, int month, int day). In the body we convert numbers to strings with std::to_string. For single-digit months and days we prepend a zero: "0" + std::to_string(month). Result: Helpers::formatDate(2024, 3, 15) returns "2024-03-15". This method is useful for log entries and reports.
Conversion with std::to_string
To convert an int to a string, use std::to_string. Example: std::to_string(2024) returns "2024". You can join strings with +.
For single-digit months and days, a zero must be prepended. The logic: std::string m = std::to_string(month); if (m.length() == 1) m = "0" + m;. So 3 becomes "03", 12 stays "12". Finally we join the parts with hyphens: std::to_string(year) + "-" + m + "-" + d. This produces a deterministic output.
Practice Add the formatDate method and call it
Take the previous lesson's solution (Helpers class has capitalize and clamp). Under public: add static std::string formatDate(int year, int month, int day). In the body, prepend a zero for single-digit months and days, then return std::to_string(year) + "-" + m + "-" + d. In main after the clamp call add std::cout << std::endl << Helpers::formatDate(2024, 3, 15);.
Starter code
#include <iostream>
#include <string>
#include <cctype>
class Helpers {
public:
static std::string capitalize(std::string text) {
if (text.empty()) return text;
text[0] = std::toupper(text[0]);
return text;
}
static int clamp(int value, int min, int max) {
if (value < min) return min;
if (value > max) return max;
return value;
}
};
int main() {
std::cout << "Ready" << std::endl;
std::cout << Helpers::capitalize("hello") << std::endl;
std::cout << Helpers::clamp(15, 0, 10);
// Add the formatDate method and call it
return 0;
}Sample solution
#include <iostream>
#include <string>
#include <cctype>
class Helpers {
public:
static std::string capitalize(std::string text) {
if (text.empty()) return text;
text[0] = std::toupper(text[0]);
return text;
}
static int clamp(int value, int min, int max) {
if (value < min) return min;
if (value > max) return max;
return value;
}
static std::string formatDate(int year, int month, int day) {
std::string m = std::to_string(month);
if (m.length() == 1) m = "0" + m;
std::string d = std::to_string(day);
if (d.length() == 1) d = "0" + d;
return std::to_string(year) + "-" + m + "-" + d;
}
};
int main() {
std::cout << "Ready" << std::endl;
std::cout << Helpers::capitalize("hello") << std::endl;
std::cout << Helpers::clamp(15, 0, 10) << std::endl;
std::cout << Helpers::formatDate(2024, 3, 15);
return 0;
}Expected output
Ready Hello 10 2024-03-15
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each call to its output
| Term | Meaning |
|---|---|
formatDate(2024, 3, 15) |
"2024-03-15" |
formatDate(2024, 12, 1) |
"2024-12-01" |
formatDate(2024, 1, 5) |
"2024-01-05" |
formatDate(2024, 10, 25) |
"2024-10-25" |
2 Which is the ISO 8601 date format?
- "15/03/2024"
- "15-03-2024"
- "03/15/2024"
- "2024-03-15" Correct answer
Explanation: ISO 8601 is YYYY-MM-DD: 2024-03-15.
3 Complete the std::to_string call
return std::____(year) + "-" + m + "-" + d;return std::to_string(year) + "-" + m + "-" + d;Explanation: std::to_string converts the number to a string.