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I'm trying to use putchar() and getchar() to read in a string of characters from the user, and then my loop will print each character three times, print a new line, etc etc, until every character in the variable "userInput" has been printed. When I try to compile my program I receive the following errors:

warning: assignment makes pointer from integer without a cast [enabled by default]
 userInput = getchar();
           ^
warning: comparison between pointer and integer [enabled by default]
 while(counter < strlen(userInput))
               ^
error: array subscript is not an integer
     putchar(userInput[counter]);
                      ^
error: array subscript is not an integer
     putchar(userInput[counter]);
                      ^
error: array subscript is not an integer
     putchar(userInput[counter]);
                      ^

How can I fix these errors? I'm new to C and can't figure out what it means by the pointer cast error, and why my counter variable isn't working.

My code is as follows:

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

int main(void)
{
    char *userInput;
    int *counter = 0;

    printf("Enter a string of characters: ");
    userInput = getchar();


    while(counter < strlen(userInput))
    {
        putchar(userInput[counter]);
        putchar(userInput[counter]);
        putchar(userInput[counter]);
        printf("\n");
        counter++;
    }    
}
A.Coder
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3 Answers3

1

I'm not really sure why you want to do this, but if I had to do it, I'll probably do it like this -

01 #include <stdio.h>
02 int main()
03 {
04     char userInput[100],c;
05     int length, i=0;
06 
07     printf("Enter a string of characters: ");
08     while(c=getchar()){
09         if(c=='\n')
10             break;
11          userInput[i++] = c;
12      }
13      userInput[i]='\0';
14      length = i;
15  
16      for(i=0; i<length; i++){
17          putchar(userInput[i]);
18          putchar(userInput[i]);
19          putchar(userInput[i]);
20          putchar('\n');
21      }
22      return 0;
23  }

I've added line numbers for better understanding. Here's what I did -

  • I don't need any other header file except stdio.h, so removed extras.
  • You probably wanted a string (array of characters), so you have to define it like in line 04, as a character array. As getchar() returns a character, assigning it to a char pointer would give errors. Additionally I declared a variable "c" which you'll see later.
  • Instead of counter, I'm using the standard i, and declared a variable length to store the string length.
  • Interesting thing in line 08, while(c=getchar()). What this does is, it keeps reading a character and storing it in the variable c as long as a character exists in the input stream (entered by the user).
  • In line 09, I'm checking if c contains a newline (i.e. the user pressed Enter/Return key). If that's the case, I stop reading the string and get out of the loop using the break keyword in line 10.
  • In line 11, I store the character c at the ith index of the userInput array, and increment i at the same time. You could do the same thing in two lines two.
  • In line 13, the value of i will be the input string's length. At the last index, I store a special character '\0' which is the null terminator. You can look it up to know more about it.
  • In line 14, I store the value of i in length variable.
  • From line 16-21, I run a simple for loop from i=0 to length, and in each iteration I print the character 3 times as you wanted to. In line 20, instead of printf(), I use the putchar() to print a new line, as '\n' is a char, just to show you.

So this does the task as you wanted to. I tried to make it as beginner friendly as I could, comment for any queries. Glad to help. :)

Aakash Choubey
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0

If you want to use a character pointer to store data, you either need to have an existing string which you can make this character pointer point to, or you need to dynamically allocate a number of bytes which can then be used to store new data.

char *string = malloc(50);

is equivalent to

char string[50];

Also the integer does not need to be a pointer if you are storing only a single value. So it should be just 

int counter=0;

In the program you have written, getchar() only takes one single character

You should use a string handling function like gets(string); to do this It will make things easier

Shaun F
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-1
  1. getchar() returns a SINGLE char as unsigned int. You have to cast it to char to avoid the warning.
  2. getchar return an int, it does not allocate anything.
  3. As told it read ONE character, so you cannot loop on it.

I think you should search for fgets or scanf or call getchar() in a loop but you will need to use a specific char to exit the loop.

fievel
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