Aligning strings equally

Question

I am trying to align these strings with their respective indexes. The strings look like this:

char *mystrings[] = {"Fred", "Augustine", "Bob", "Lenny", "Ricardo"};

and my output looks like this:

Fred 0
Augustine 1
Bob 2
Lenny 3
Ricardo 4

But I am after some thing like this:

Fred       0
Augustine  1
Bob        2
Lenny      3
Ricardo    4

Whereby the indexes are aligned the same. I'm just trying to make it more readable. This is what my code looks like so far:

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

int
main(void) {
    int i;
    char *mystrings[] = {"Fred", "Augustine", "Bob", "Lenny", "Ricardo"};

    for (i = 0; i < 5; i++) {
        printf("%s %d\n", mystrings[i], i);
    }

    return 0;
}

Is there a way I can do this? Like compare the indexes with the longest string, and then make the spaces for the integers like that?

Answer 1

Extra loop to calculate the max width, then use the * printf flag to take the width from an argument (which is multiplied by -1 to cause left justification)

char *mystrings[] = {"Fred", "Augustine", "Bob", "Lenny", "Ricardo"};
int width = 0;
for (int i = 0; i < sizeof(mystrings)/sizeof(char*); i++) {
    width = strlen(mystrings[i]) > width? strlen(mystrings[i]) : width;
}

for (int i = 0; i < sizeof(mystrings)/sizeof(char*); i++) {
    printf("%*s %d\n", -1 * width, mystrings[i], i);
}

Answer 2

You need to specify a width for the string in the format specification.
Then, you need to use the - specifier to indicate that you want the output to be left justified.

Using

printf("%-10s %d\n", mystrings[i], i);

will use 10 characters for mystrings[i] and will left justify the output.

Hard coding a number like that will be a problem if you don't know the lengths of the strings. To make your program a bit robust, you can compute the maximum length of the strings and then compute the format string from that.

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

#define MAXSIZE 5

int main(void) {
   int i;
   char *mystrings[MAXSIZE] = {"Fred", "Augustine", "Bob", "Lenny", "Ricardo"};

   int maxLen = 0;
   for (i = 0; i < MAXSIZE; i++) {
      int len = strlen(mystrings[i]);
      maxLen = (len > maxLen) ? len : maxLen;
   }

   char formatString[50];
   sprintf(formatString, "%%-%ds %%d\n", maxLen + 1);

   for (i = 0; i < MAXSIZE; i++) {
      printf(formatString, mystrings[i], i);
   }

   return 0;
}

Output

Fred       0
Augustine  1
Bob        2
Lenny      3
Ricardo    4