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#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
#define GEN_MAX 1000000000
static int tenpow(int pow) {
int base = 10;
int ret = 1;
while (pow) {
if (pow & 0b1)
ret *= base;
base *= base;
pow >>= 1;
}
return ret;
}
static char get_at_pos(unsigned int n, int pos) {
n /= tenpow(pos);
return n % 10;
}
int main(int argc, char *argv[]) {
srand(time(NULL));
int arr[10] = {0};
unsigned int gen;
int iters, pos;
if (argc == 3) {
iters = atoi(argv[1]);
pos = atoi(argv[2]);
if (!iters || !pos) goto fail;
} else {
fputs("Iterations: ", stdout);
if (!scanf("%i", &iters)) goto fail;
fputs("Position (10^N): ", stdout);
if (!scanf("%i", &pos)) goto fail;
}
for (int _ = 0; _ < iters; ++_) {
gen = rand() % GEN_MAX;
#ifdef PRINT_GENERATED
printf("%i\n", gen);
#endif
switch (get_at_pos(gen, pos)) {
case 0: ++arr[0]; break;
case 1: ++arr[1]; break;
case 2: ++arr[2]; break;
case 3: ++arr[3]; break;
case 4: ++arr[4]; break;
case 5: ++arr[5]; break;
case 6: ++arr[6]; break;
case 7: ++arr[7]; break;
case 8: ++arr[8]; break;
case 9: ++arr[9]; break;
default: __builtin_unreachable();
}
}
printf("count of numbers at position %i:\n", pos);
for (int i = 0; i < 10; ++i)
printf("\t%i: %i\n", i, arr[i]);
return EXIT_SUCCESS;
fail:
fputs("Input a valid number\n", stderr);
return EXIT_FAILURE;
}
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