What not to do and what to do to get correct answer

Question

1.00/5 (1 vote)

See more:

#include<stdio.h>
#include<string.h>
int main()
{
    int t,n,len=0,c=0;
    scanf("%d",&t);
    for(int i=1;i<=t;i++){
        scanf("%d",&n);
        len=sizeof(n);
        char str[len];
        sprintf(str,"%d",n);
        for(int k=0;k<len;k++){
           if(str[k]=="4"){
               c++;
           }
        }printf("%d\n",c);
    }
    return 0;
}

What I have tried:

I want to take a test case and number and then want to find 4 between those numbers. So firstly I took the test case and number then I convert the number to a string and want to be checked one by one char to find 4 between the converted string. For this, I wrote a program like the given photo but I program isn't giving only 0 even if there are 4, now what to do and where is my problem

Posted 19-May-22 7:00am

Fardin Khan_451

Updated 19-May-22 10:12am

v2

Add a Solution

3 solutions

Solution 1

Compiling successfully does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:

Input   Expected output    Actual output
  1            2                 1
  2            4                 4
  3            6                 9
  4            8                16

Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:

C

int Double(int value)
   {
   return value * value;
   }

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

Posted 19-May-22 8:03am

OriginalGriff

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Rick York · Accepted Answer · 2022-05-19T10:12:00

There are a few things wrong with your code and they have to deal with how you handle the string. First, as mentioned previously, this is incorrect use of the sizeof operator. The character buffer variable, str, needs to be bigger than that. Size of an int will return 4 in a 32 or 64-bit environment and that means you string can hold three digits at most so an input of 9999 will overflow the buffer. A four-byte integer can old values up to 2G which has ten digits. For that reason it is better to make the buffer something like 16 characters long. If you want to handle 64-bit integers then the buffer will need to be at least 20 characters. A length of 24 would allow you to safely handle both of those types. Also, since you are looking at every character in the string what you really want is the length of the character string, not the size of an integer. Since sprintf returns the number of characters it writes that is the value want to use. As mentioned previously, you want to compare with the character 4 and not the string.

If I make those changes, your code could look like this :

C++

int main()
{
    int t,n,len,c=0;
    char str[ 24 ];
    scanf( "%d", &t );
    for(int i=1;i<=t;i++)
    {
        printf( "enter string %d : ", i );
        scanf( "%d", &n );

        c = 0;  // reset the counter for every input string

        len = sprintf( str, "%d", n );
        for( int k=0; k < len; k++ )
        {
           if( str[k]== '4' )
           {
               c++;
           }
        }
        printf("%d instances were found\n", c );
    }
    return 0;
}

Greg Utas · Accepted Answer · 2022-05-19T08:05:00

It looks like you think that sizeof(n) tells you how many digits there are in n. But it actually tells you how many bytes are in an int, and the result will be the same every time (probably 4). So if you enter a 5-digit number, sprintf will fail. Just use str[9] or however many digits you want to allow, and then use k<strlen(str) in your loop.

Also, str[k]=="4" compares a char to a string. I don't know if that works, because I've never written it that way (I only write C++, where it won't even compile). Whether it works or not, you should write str[k]=='4'.

What not to do and what to do to get correct answer

3 solutions

Solution 3

Solution 2

Solution 1

Add your solution here

Preview 0