getNumDisplayWidth

main.cpp

#include <cstdio>
#include <cmath>
#include <array>

static unsigned getNumDisplayWidth(unsigned N) {
  if (N < 10)
    return 1;
  if (N < 100)
    return 2;
  if (N < 1000)
    return 3;
  if (N < 10000)
    return 4;
  if (N < 100000)
    return 5;
  if (N < 1000000)
    return 6;
  if (N < 10000000)
    return 7;
  printf("No source file should have more than 10 million lines");
  return 0;
}

static unsigned getNumDisplayWidth2(unsigned N) {
    return ceil(log10(N+1));
}

int main(int argc, char* argv[]) {
    std::array<int, 14> Ns = {9, 10, 99, 100, 999, 1000, 9999, 10000, 99999, 100000, 999999, 1000000, 9999999, 10000000};
    for (auto N:Ns){
        printf("getNumDisplayWidth  (%10d) = %d\n", N, getNumDisplayWidth(N));
        printf("getNumDisplayWidth2 (%10d) = %d\n", N, getNumDisplayWidth2(N));
    }
    return 0;
}

output.txt

getNumDisplayWidth  (         9) = 1
getNumDisplayWidth2 (         9) = 1
getNumDisplayWidth  (        10) = 2
getNumDisplayWidth2 (        10) = 2
getNumDisplayWidth  (        99) = 2
getNumDisplayWidth2 (        99) = 2
getNumDisplayWidth  (       100) = 3
getNumDisplayWidth2 (       100) = 3
getNumDisplayWidth  (       999) = 3
getNumDisplayWidth2 (       999) = 3
getNumDisplayWidth  (      1000) = 4
getNumDisplayWidth2 (      1000) = 4
getNumDisplayWidth  (      9999) = 4
getNumDisplayWidth2 (      9999) = 4
getNumDisplayWidth  (     10000) = 5
getNumDisplayWidth2 (     10000) = 5
getNumDisplayWidth  (     99999) = 5
getNumDisplayWidth2 (     99999) = 5
getNumDisplayWidth  (    100000) = 6
getNumDisplayWidth2 (    100000) = 6
getNumDisplayWidth  (    999999) = 6
getNumDisplayWidth2 (    999999) = 6
getNumDisplayWidth  (   1000000) = 7
getNumDisplayWidth2 (   1000000) = 7
getNumDisplayWidth  (   9999999) = 7
getNumDisplayWidth2 (   9999999) = 7
No source file should have more than 10 million linesgetNumDisplayWidth  (  10000000) = 0
getNumDisplayWidth2 (  10000000) = 8