'Else if' is not working

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[Updated]
I was trying to solve this problem:
1098 - Sequence IJ 4 - URI Online Judge[^]

I used else if statement to print integer when needed. It worked for two conditions but it's not working for the third condition. The code I wrote is given below.
[sorry for my bad English]

What I have tried:

#include<stdio.h>
int main(){
int a,b,c,d,e, about;
double x,y,z, sum;
double i, j;
for(i=0; i<=2; i=i+0.2){
    for(j=1; j<=3; j++){

        if(i==0.0){
            printf("%.0lf %.0lf\n", i, j+i);
        }else if(i==1.0){
        printf("%.0lf %.0lf\n", i, j+i);
        }else if(i==2.0){
        printf("%.0lf %.0lf\n", i, j+i);
        }else{
        printf("%.1lf %.1lf\n", i, j+i);
        }
    }
}
return 0;
}

Posted 20-Oct-21 17:18pm

Jahirul Sarker

Updated 26-Oct-21 19:15pm

v3

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3 solutions

Solution 2

Quote:
I used else if statement to print integer when needed. It worked for two conditions but it's not working for the third condition. The code I wrote is given below.

Because your code says so:

C++

#include<stdio.h>
int main(){
int a,b,c,d,e, about;
double x,y,z, sum;
double i, j;
for(i=0; i<2; i=i+0.2){ // i is never equal to 2.0 in the loop
    for(j=1; j<=3; j++){

        if(i==0.0){
            printf("%.0lf %.0lf\n", i, j+i);
        }else if(i==1.0){
        printf("%.0lf %.0lf\n", i, j+i);
        }else if(i==2.0){ // so this condition is never met
        printf("%.0lf %.0lf\n", i, j+i);
        }else{
        printf("%.1lf %.1lf\n", i, j+i);
        }
    }
}
return 0;
}

[Update]

Quote:
1st two outputs are integers... But the third printf is printing float... that's why I am telling that third statement is not working.

Stop guessing, make sure, try with this code.

C++

        if(i==0.0){
            printf("A %.0lf %.0lf\n", i, j+i);
        }else if(i==1.0){
            printf("B %.0lf %.0lf\n", i, j+i);
        }else if(i==2.0){
            printf("C %.0lf %.0lf\n", i, j+i);
        }else{
            printf("D %.1lf %.1lf\n", i, j+i);
        }
    }
}
return 0;
}

Use the letter in each printf to distinguish which printf was used.
Ur learn debugger.

Posted 20-Oct-21 20:42pm

Patrice T

Updated 23-Oct-21 20:37pm

v2

Comments

Jahirul Sarker 21-Oct-21 9:22am

I changed it to for(i=0; i<=2; i=i+0.2).
But it's not working. Same problem remains. Third condition is not working

Patrice T 21-Oct-21 9:57am

How can you know which condition matched since the 3 first output are same ?

Jahirul Sarker 24-Oct-21 2:23am

1st two outputs are integers... But the third printf is printing float... that's why I am telling that third statement is not working.

Patrice T 24-Oct-21 2:59am

See updated solution.

Solution 3

Here's the solution:

#include<stdio.h>

int main(){
double i,j;


for(i=0; i<=2; i=i+0.2){
    for(j=1; j<=3; j++){

        if (i<0.1){
            printf("I=%.0lf J=%.0lf\n", i, j+i);
        }else if(i>0.9&&i<1.1){
        printf("I=%.0lf J=%.0lf\n", i, j+i);
        }else if(i>1.8&&i<2.1){
        printf("I=%.0lf J=%.0lf\n", i, j+i);
        }else{
        printf("I=%.1lf J=%.1lf\n", i, j+i);
        }
    }
}
return 0;
}

Posted 26-Oct-21 19:15pm

Jahirul Sarker

Comments

CHill60 27-Oct-21 4:58am

For every single one of your questions you have subsequently posted a solution and marked it as the "best answer". That is actually quite rude, and devalues the contribution from other members that led you to that solution.
Some members will also see that as "reputation point hunting" and consider it to be abuse of the site - that could lead to your account being suspended.
Please mark the most helpful solution as the "best" - you could even be guided by the rest of the community - at the time of writing Solution 1 has 5 upvotes

Jahirul Sarker 27-Oct-21 6:47am

Thank you. Honestly, I wasn't aware of that. I was stupid. I wasn't aware of the points.
I will never repeat this mistake again.

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Rick York · Accepted Answer · 2021-10-20T19:25:00

What is happening is you are bumping up against small, numerical errors in floating point values. The value of i after ten 0.2s were added will not match 2.0 exactly. It probably will out to be about eight or nine decimal places but not exactly. If you want to see this more closely, add this statement right before the if :

C++

printf( "i is %18.16f\n", i );

That will show you the value of i to sixteen decimal places.

To get around this you need to allow for a tolerance which is often called epsilon. There are lots of ways to deal with this and here is one option. Write a function called CloseEnough or something similar. Here's how it might look.

C++

// function will return 1 if close enough, 0 if not

int CloseEnough( double value1, double value2 )
{
    double delta = fabs( value1 - value2 );  // obtain absolute value of difference
    return ( delta < 1.0E-6 ) ? 1 : 0;       // compare with epsilon value
}

In this logic the epsilon value is 1E-6 or 0.000001. When comparing with 2.0 it will return 1 if the value is between 1.999999 and 2.000001 and zero if it isn't. This not an particularly general purpose solution because it will give bad results for very large and very small numbers but for values of the magnitude of yours it should be suitable.