Как в C++ увеличить число символов, занимаемых числом?
#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
    cout << 300 << endl;
    cout << setw(3) << 3 << endl;
    cout << setfill('0') << setw(3) << 3 << endl;
    return 0;
}
Вывод[guest@localhost cpp]$ .iso++ t.cpp -o t
[guest@localhost cpp]$ ./t
300
  3
003
[guest@localhost cpp]$
Пример отсюда
TL;DR: printf("%03d") или printf("%3d")/* printf example */
#include <stdio.h>

int main()
{
   printf ("Characters: %c %c \n", 'a', 65);
   printf ("Decimals: %d %ld\n", 1977, 650000L);
   printf ("Preceding with blanks: %10d \n", 1977);
   printf ("Preceding with zeros: %010d \n", 1977);
   printf ("Some different radices: %d %x %o %#x %#o \n", 100, 100, 100, 100, 100);
   printf ("floats: %4.2f %+.0e %E \n", 3.1416, 3.1416, 3.1416);
   printf ("Width trick: %*d \n", 5, 10);
   printf ("%s \n", "A string");
   return 0;
}Characters: a A
Decimals: 1977 650000
Preceding with blanks:       1977
Preceding with zeros: 0000001977
Some different radices: 100 64 144 0x64 0144
floats: 3.14 +3e+000 3.141600E+000
Width trick:    10
A string