Error: expected declaration specifiers or '...' before string constant [puts() and gets() statement errors

Question

After compiling my program of Dice Roll, I got this error. What is wrong with the code?

Also before I was using gets() instead of scanf() command, but because of that I got this error - passing argument 1 of 'gets' makes pointer from integer without a cast So I removed the gets() command and used scanf and then there was no error regarding scanf().

What is the reason for getting these two errors?

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Ok, so as per the answer I got to know how I should have used the gets() command and why I shouldn't use it instead should use scanf(). So, I made the changes. Though I have encountered two new errors, this time it's related to the delay() command that I used.

Errors: undefined reference to delay |error: ld returned 1 exit status|

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OK so I solved my last errors by using Sleep() command from windows.h library instead of Delay() command. The programs was compiled. But still there is a runtime error in the program, it works well till getting the roll1 but then it just print the next two statement and terminated the programs without taking a input for the guess.

It skips all the code after printf("Will it be Higher/Lower or the same? (press H/L/S)\n"); and directly terminates the program.

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Ok So I solved above problem adding a whitespace before the "%c" in scanf(" %c", &nextGuess); statement. (Little things xD) Now only problem is that my toupper() command is not working.

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


int main()
{
    int i, roll1=0, roll2=0, NumberOfRolls, RandomNUM1[50], RandomNUM2[50];
    char nextGuess;

    puts("Welcome to the Dice Roll Game");
    puts("How many times do you want to roll a dice?");
    scanf("%d", &NumberOfRolls);

    for( i=1; i<=NumberOfRolls; i++ ) {
        RandomNUM1[i] = ( rand()%6 ) + 1;
        roll1 += RandomNUM1[i];
    }

    printf("\nYou Got %d in your first roll!\n", roll1);
    Sleep(3000);
    printf("\nLet's see if you can guess the value of next roll.\n");
    printf("Will it be Higher/Lower or the same? (press H/L/S)\n");
    scanf(" %c", &nextGuess);
    toupper(nextGuess);

        for( i=1; i<=NumberOfRolls; i++ ) {
        RandomNUM2[i] = ( rand()%6 ) + 1;
        roll2 += RandomNUM2[i];
    }

    if(nextGuess=='H'){
        if(roll1<roll2){
            printf("You are such a player, you guessed it right! It's %d", roll2);
        }
        else if(roll1>roll2){
            printf("Uh-Oh! Bad Luck! First roll was higher, It's %d", roll2);
        }
        else if(roll1==roll2){
            printf("Uh-Oh! Bad Luck! Both the rolls are same, It's %d", roll2);
        }

    }

    if(nextGuess=='L'){
        if(roll1>roll2){
            printf("You are such a player, you guessed it right! It's %d", roll2);
        }
        else if(roll1<roll2){
            printf("Uh-Oh! Bad Luck! First roll was lower, It's %d", roll2);
        }
        else if(roll1==roll2){
            printf("Uh-Oh! Bad Luck! Both the rolls are same, It's %d", roll2);
        }

    }

    if(nextGuess=='S'){
        if(roll1==roll2){
            printf("You are such a player, you guessed it right! It's %d", roll2);
        }
        else if(roll1>roll2){
            printf("Uh-Oh! Bad Luck! First roll was higher, It's %d", roll2);
        }
        else if(roll1<roll2){
            printf("Uh-Oh! Bad Luck! Second roll is higher, It's %d", roll2);
        }

    }

        return 0;
}

Answer 1

The gets function reads a string (till the next newline character) from stdin, therefore it asks for a char pointer (char*) to an area of memory where it can put all the characters read including string terminator. The mistake you made is to pass to that function a pointer to int, therefore not only you get a compiler error because you tried to pass an int pointer to gets (for which there are none implicit conversions), but even if it compiled, it would not have worked as you expected because it would put all the characters (which have a size of one byte - most of the times) in that area of memory encoded as chars. That means that when you try to dereference one using a pointer to int, the characters are "read like they were an int"!

There is an example (supposing 1-byte chars, 4-bytes int and a little endian machine and that there is an implicit cast from int* to char* which does not exist and hopefully will never exist):

int num
gets(&num);

if I input 123 in stdin, the memory area pointer by num is large enough to contain the string, but it would contain (exadecimal representation):

0x31|0x32|0x33|0x00

because the string is 3 characters long, ASCII code for '1' is 0x31, for '2' is 0x32, and for '3' is 0x33 and terminates with '\0'!! Then, when you try to dereference it you get this int (binary representation - supposing a little endian machine):

00000000|00110001|00110010|00110011

which is not the int value 123 but instead ‭3224115‬. Which is not what you wanted to get.

When you use the scanf function, you pass to that function a format string which tells it how to interpret the next arguments passed to it and performs the appropriate conversions between the string read to the right type you specified. That means that you should still pay attention to what you tell to the scanf function while you write the format string (if you tell it to read a string and pass to it a pointer to int, the program will probably crash), but it performs the appropriate conversions for you, if you write the format string correctly.

That's why with scanf everything works perfectly (you're reading an int and you specified "%d" as format string), whereas with gets it does not compile to avoid serious mistakes.

I also would like to remark some points of this answer:

• The example is just for didactic purposes and the code provided does not work indeeed. The fact that I supposed that it compiles is for didactic purposes; obviously, the code provided in that example does not compile
• If, in that example, we input a string larger than 3 characters (which are four if we include the null terminator) or the int (char) type contains less (more) than 4 (1) byte, the program would have crashed because we corrupted other areas of memory
• The reference is more expert than me in techincal stuff, so here are the links to the gets function and the scanf function: gets, scanf (and the ASCII Table is useful too)
• You could use the gets function together with the atoi function to parse the string read from gets (using a char pointer to a free area of memory large enough to contain the string, which is pretty hard to allocate (*)) to an int, but scanf is the best approach.

(*) Remember: if you allocate an area of memory that contains 20 chars, the user will input 21 chars. The atoi function fails, but the worst thing is that you have a buffer overflow (and can be a high security issue if your program runs under root permissions).

Answer 2

You have a stray ,

At the 2nd line of your main, you declare char nextGuess, instead of char nextGuess;

The compiler tells you it expects specifiers or ... after , so either you add these, or you end the line properly with;.

And for the other problem you mention:

passing argument 1 of 'gets' makes pointer from integer without a cast

Since gets argument should be char *str and you didn't provide it.

You can fix that by, for example:

char tmp_NumberOfRolls[10];
gets(tmp_NumberOfRolls);  
NumberOfRolls = atoi(tmp_NumberOfRolls);

but I prefer the scanf solution

PS: (in a now edited version of the code) ***//Error Line*** is not a comment (at least, not all of it) since the *** is still counted as part of the code and will cause an error. Either move the // a bit to the left or enclose that whole part with /* ... */