Question

I’m trying to write a function to fill an array with 40 random uppercase letters. I attempted to fill the array and print it but I’m not getting any output.

Thank you in advance.

#include <stdio.h>
#include <stdlib.h>

void fillS1(char y[]);

int main(int argc, const char * argv[])
{
char s1[40];
int n;

fillS1(&s1[40]);

for (n = 0; n < 41; n++) {
    printf("%s", s1);
}


return 0;
}

void fillS1(char y[40]){

int x = 1;

while (x < 41) {
    x = rand() % 26;
    x = 2 + 'A';
    x = y[x];
    x++;
}


}

Answer 1

I would just code

void fill_string_40(char str[])
{
   for (int i=0; i<40; i++)
     str[i] = 'A' + random() % 26;
   str[40] = (char)0; // (char)0 is equal to use '\0'
}

and use it as (e.g. in your main)

{ char s[41];
  fill_string_40(s);
  printf("%s\n", s);
}

Notice that you need an extra byte for the null terminating character. Ad we are assuming some ASCII compatible char encoding. A more portable way could have been

str[i] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"[random() % 26];

since literal strings are constant arrays of chars.

If you code in C++, see the standard <random> header file. If you code for Linux, see random(4) and getrandom(2), perhaps use it with srandom(3). Read also about the Mersenne Twister