Input to array of strings won't show? - c

Question

I'm in C and I'm supposed to have an input of numbers (don't know how many) formatted into one column without storing them into an array of integers. I can't figure out why my code won't read the input and out put it. Please help.
#include <stdio.h>
#include <stdlib.h>
int main() {
int i;
char *nums[400];
for (i=0; i<nums; i++) {
scanf(nums[i]);
printf( "%.*s", 3, nums[i] );
}
return 0;
}

Answer 1

You have an array of 400 pointers, but you've never initialized them. Instead, you could declare a 2-dimension array:
char nums[400][4];
Then you're trying to use nums as a limit to the for loop. What you actually want is the number of elements in nums, which is sizeof(nums)/sizeof(nums[0]); or you could define a macro that specifies the size of the array.
Next, you left out the format string argument to scanf().
#include <stdio.h>
#include <stdlib.h>
#declare SIZE 400
int main()
{
int i;
char *nums[SIZE][4];
for(i=0; i<SIZE; i++){
scanf("%3s", nums[i]);
printf( "%.*s", 3, nums[i] );
}
return 0;
}

Answer 2

As Baramar correctly and thoroughly explained your main problems, I think I might have a different understanding of your problem. You want a given string of number, e.g.: 2134567896543245678 and print it out in a single column, neatly formated in rows of three digits each like that:
213
456
789
654
324
567
8
without an intermittent array of integers.
That could be done like e.g.: this
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFER_SIZE 512
int main()
{
int res;
// for the scanf input, set all to '\0'
char buffer[BUFFER_SIZE + 1] = { '\0' }, *idx;
size_t len, i;
// restrict max-size to BUFFER_SIZE
res = scanf("%512s", buffer);
if (res != 1) {
exit(EXIT_FAILURE);
} else {
if (strcmp(buffer, "exit") == 0) {
exit(EXIT_SUCCESS);
}
// TODO: check if the buffer contains all digits
len = strlen(buffer);
idx = buffer;
for (i = len; i >= 3; i -= 3, idx += 3) {
printf("%.3s\n", idx);
}
// last entries, if any
if (*idx != '\0') {
printf("%s\n", idx);
}
}
exit(EXIT_SUCCESS);
}
If you get actual integers in a row like e.g.: 12 3123 23478 34 5456 567456 567 678 you can use something like that:
EDIT
After the comment by the OP to use floating points I changed the code to accept input of the form:
24722.319352 51433.662233
56087.991042 49357.684934 67875.375848 68421.563197
54521.615295
22744.470483
38097.001461 80878.250982
92131.575748 7217.137271
20750.671365 7620.695008 37118.391541 28655.609469 46885.110202 87114.202312
46462.577299
20557.716648
And the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXNUM 400
int main()
{
int res;
int i = 0, m;
// input and two temporary variables
double in, in1, in2;
for (m = 0; m < MAXNUM; m++) {
res = scanf("%lf", &in);
if (res != 1) {
break;
} else {
switch (i) {
case 0:
// set value of first temporary variable to input
in1 = in;
// increment indicator indicating position in output row
i++;
break;
case 1:
in2 = in;
i++;
break;
case 2:
// print the three numbers and a newline
fprintf(stdout, "%f %f %f\n", in1, in2, in);
// reset counter
i = 0;
break;
}
}
}
// if there are still numbers, print them
if (i != 0) {
if (i == 1) {
fprintf(stdout, "%f\n", in1);
} else {
fprintf(stdout, "%f %f\n", in1, in2);
}
}
exit(EXIT_SUCCESS);
}
Try it out with
$ gcc-4.9 -O3 -g3 -W -Wall -Wextra -std=c11 sc.c -o sc
$ ./sc < floatin
24722.319352 51433.662233 56087.991042
49357.684934 67875.375848 68421.563197
54521.615295 22744.470483 38097.001461
80878.250982 92131.575748 7217.137271
20750.671365 7620.695008 37118.391541
28655.609469 46885.110202 87114.202312
46462.577299 20557.716648
If you enter less than 400 entries you need to end with EOF which can be triggered in most Unix shells with ctrl+d or set an entry to end the entries like e.g.: -1 if all you have is positive numbers and check for it to break out of the loop. If you submit a file like in the example above it works automatically.