#include <stdio.h>
#include <ctype.h> // for isdigit()
#include <string.h> // for strlen()
/*
extract_digits
--------------
Scans a string and copies every digit ('0'–'9') into an output buffer.
Parameters:
src - input string to scan
dest - output buffer to store extracted digits
Notes:
- The caller must ensure 'dest' is large enough.
- The function writes a null terminator at the end.
*/
void extract_digits(const char *src, char *dest) {
size_t write_index = 0;
// Walk through each character in the string
for (size_t i = 0; src[i] != '\0'; i++) {
// Use the standard library's classification function
// to check whether the current character is a digit.
if (isdigit((unsigned char)src[i])) {
dest[write_index++] = src[i];
}
}
// Properly terminate the resulting string
dest[write_index] = '\0';
}
int main(void) {
const char *str = "5 ruby8go 9001 c c++ 17python";
// Allocate a buffer large enough to hold all digits.
// Worst case: every character is a digit.
char digits[strlen(str) + 1];
// Extract digits from the input string
extract_digits(str, digits);
// Display the result
printf("Original: %s\n", str);
printf("Digits: %s\n", digits);
return 0;
}
/*
run:
Original: 5 ruby8go 9001 c c++ 17python
Digits: 58900117
*/
