[SOLVED] Simple IF statement not flowing. Why?

cryingthug · 01-21-2012, 04:51 PM

Whenever I select a number that is too low the "else" section runs. If I select a number that is too high the "else" line is not run. Why???

Code:

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

main(){

    int num = 6;
    int answer = 0;

    printf("THIS IS THE NUMBER GUESSING GAME.\n\n");
    printf("Select a number between 1 and 10.\n");
    scanf("%d", &answer);

    if(isdigit(answer))
        if(answer == num){
            printf("You guessed correctly!\n");
        }        
        if(answer < num){
            printf("You guessed too low.\n");
        } 
        if(answer > num){
            printf("You guessed too high.\n");
        } 
        // This line will run no matter what.
        else{
             printf("Please select a number.\n");
    }

}

Doc CPU · 01-21-2012, 05:18 PM

Hi there,

Quote:

Originally Posted by cryingthug

Whenever I select a number that is too low the "else" section runs. If I select a number that is too high the "else" line is not run. Why???

because each of the if statements is considered separately, while you seem to consider them related. They're not.

Code:

        if(answer == num){
            printf("You guessed correctly!\n");
        }        
        if(answer < num){
            printf("You guessed too low.\n");
        } 
        if(answer > num){
            printf("You guessed too high.\n");
        } 
        // This line will run no matter what.
        else{
             printf("Please select a number.\n");
    }

If you guess too low, i.e. answer<num, the last of the if statements is not true, so the else branch is executed.
But honestly, what is your intention - in words, not in code? Whatever you enter as answer, it is either less than, or greater than, or equal to num. There is no other situation that you might want to catch with your else statement.
Think again about the logics in your code ...

[X] Doc CPU

Dark_Helmet · 01-21-2012, 10:20 PM

An illustrative problem lies at the beginning of the if-else sequence:

Code:

    if(isdigit(answer))

The isdigit() function is meant to take a single char variable--not an int. The purpose of the isdigit() function is to verify that one or more characters in a string contain a digit (i.e. 0-9).

For instance, take the following code:

Code:

#include <stdio.h>

int main( int argc, char *argv() )
{
  char charNumber='9';
  int  intNumber=9;

  if( charNumber == intNumber )
    printf( "The values match!\n" );
  else
    printf( "The values ARE NOT EQUAL!\n" );

  return 0;
}

If you run the above code, you will get "The values ARE NOT EQUAL!" for output. The char representation of 9 is a numeric value from the ASCII table. The int representation of 9 is the binary value of 9.

All of this to say two things:
1. It appears that the program is intended to do some user-input verification.
2. Assuming #1 is true, the "Please select a number." should be moved out of the interior if-else clause to serve as the else for the isdigit()/input verification code.

kalleanka · 01-24-2012, 04:30 AM

Put the block in the same tab and its easier to see the blocks like

{

}

Code:

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

main()
{

    int num = 6;
    int answer = 0;

    printf("THIS IS THE NUMBER GUESSING GAME.\n\n");
    printf("Select a number between 1 and 10.\n");
    scanf("%d", &answer);

    if(isdigit(answer))
    {
        if(answer == num)
        {
            printf("You guessed correctly!\n");
        } 
       
        if(answer < num)
        {
            printf("You guessed too low.\n");
        } 

        if(answer > num)
        {
            printf("You guessed too high.\n");
        } 

    }else
    {
        printf("Please select a number.\n");
    }
}

and you have to fix the isdigit .

chidam · 01-25-2012, 05:25 AM

One small suggestion.
Use else-if in this case. because you are unnecessarily executing if statements
If first if-statements is true then there is no need of executing the following if statements

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

main()
{

int num = 6;
int answer = 0;

printf("THIS IS THE NUMBER GUESSING GAME.\n\n");
printf("Select a number between 1 and 10.\n");
scanf("%d", &answer);

if(isdigit(answer))
{
if(answer == num)
{
printf("You guessed correctly!\n");
}

else if(answer < num)
{
printf("You guessed too low.\n");
}

else if(answer > num)
{
printf("You guessed too high.\n");
}

}else
{
printf("Please select a number.\n");
}
}

cryingthug · 05-20-2012, 12:14 PM

Thank you all for your help! I figured it out thanks to you.