why doesn't it scanf a second time when I call the main() function? | Together C & C++ | Page 1

noble geyser Oct 21, 2022, 4:26 PM

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https://onlinegdb.com/nHASuqC74
since it doesnt scanf a second time NumCheck stays at 0 and it breaks into an infinite loop

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carmine gustBOT Oct 21, 2022, 4:26 PM

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elfin gorge Oct 21, 2022, 4:34 PM

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noble geyser https://onlinegdb.com/nHASuqC74 since it doesnt scanf a second time NumCheck sta...

main int not to be called , main its automatic call wen app runs. its app entry point

mint rock Oct 21, 2022, 4:35 PM

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you have a userinput function, but you don't use it when taking input for numcheck

noble geyser Oct 21, 2022, 4:35 PM

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so I cant call main

mint rock Oct 21, 2022, 4:35 PM

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noble geyser so I cant call main

main is automatically called when you run the program

noble geyser Oct 21, 2022, 4:36 PM

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mint rock you have a userinput function, but you don't use it when taking input for numche...

yeah the first number is not in there

mint rock Oct 21, 2022, 4:36 PM

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also, you have an infinite loop

noble geyser Oct 21, 2022, 4:36 PM

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so instead of calling main I should make another loop

mint rock Oct 21, 2022, 4:36 PM

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"while(1)" will run forever

noble geyser Oct 21, 2022, 4:36 PM

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mint rock "while(1)" will run forever

thats intentional

mint rock Oct 21, 2022, 4:36 PM

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what do you want to do

noble geyser Oct 21, 2022, 4:36 PM

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calc

mint rock Oct 21, 2022, 4:37 PM

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calculate what

noble geyser Oct 21, 2022, 4:37 PM

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Im trying to make a calc

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the first number is not in UserInput and thats intentional

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second number onwards will be in there

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its so i dont end up repeating asking for 1st num input again and again

mint rock Oct 21, 2022, 4:38 PM

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i see

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as it is, the program is kinda confusing

noble geyser Oct 21, 2022, 4:39 PM

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so the main thing Im trying to do rn is figure out how to filter out non numerical inputs

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but when I loop it the scanf function doesnt seem to work?

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for some odd reason

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see if the scanf function works it'd ask for an input

mint rock Oct 21, 2022, 4:40 PM

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noble geyser for some odd reason

int NumCheck = scanf("%lf", &Result[0]);

noble geyser Oct 21, 2022, 4:41 PM

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but no, it just infinite loops

mint rock Oct 21, 2022, 4:41 PM

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this does not do what you think it does

noble geyser Oct 21, 2022, 4:41 PM

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mint rock this does not do what you think it does

so it does not tell me if the input was the right value?

mint rock Oct 21, 2022, 4:41 PM

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scanf returns the number of input items successfully matched

noble geyser Oct 21, 2022, 4:42 PM

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right.

mint rock Oct 21, 2022, 4:42 PM

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so since you're only matching one input

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NumCheck will always be equal to 1

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if there was an input

noble geyser Oct 21, 2022, 4:42 PM

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and NumCheck would always be equal to 0 if there wasnt a valid input?

mint rock Oct 21, 2022, 4:43 PM

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in this case

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yes

noble geyser Oct 21, 2022, 4:43 PM

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is there a way for me to reset NumCheck

mint rock Oct 21, 2022, 4:43 PM

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you can have it inside the loop for one

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but also, you can just skip having the numchecker function entirely

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and check the return value of scanf

noble geyser Oct 21, 2022, 4:44 PM

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mint rock and check the return value of scanf

how would that help?

mint rock Oct 21, 2022, 4:44 PM

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you want to know if the user entered a valid number

noble geyser Oct 21, 2022, 4:44 PM

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yes

mint rock Oct 21, 2022, 4:45 PM

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instead of doing numChecker(numcheck)

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you could just do if (numcheck == 1)

noble geyser Oct 21, 2022, 4:45 PM

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okay yeah that makes sense

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but it would still break, no?

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yep

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still breaks

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fuckk

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seems like I also broke the calc

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while trying to add the num checking fucntionality

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https://onlinegdb.com/meUBfSUst
[broken] with the broken num checking

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[Fixed] without broken num checking
https://onlinegdb.com/POw8PSClM

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Im going to hit the sack for now

mint rock Oct 21, 2022, 5:00 PM

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noble geyser [Fixed] without broken num checking https://onlinegdb.com/POw8PSClM

working fine here

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i assume you mean you fixed it completely?

noble geyser Oct 21, 2022, 5:02 PM

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mint rock i assume you mean you fixed it completely?

I only fixed it by removing the num checking feature

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I still want to try and add that If I could

mint rock Oct 21, 2022, 5:02 PM

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ah i see

noble geyser Oct 21, 2022, 5:02 PM

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so once for first input

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and one in UserInput

mint rock Oct 21, 2022, 5:03 PM

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hmm

noble geyser Oct 21, 2022, 5:06 PM

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im actually going to go get some rest now

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ok so I figured something out

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https://onlinegdb.com/uIXULyWP_

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I could break out of the while loop

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so it would still break the calc, but it would now say that it did

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ig thats the best i can do for now

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C's hard

mint rock Oct 21, 2022, 5:13 PM

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noble geyser ig thats the best i can do for now

how about this

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#include <stdio.h>

int UserInput(char* Operation, double* Num){
    printf("\nInput Operation: ");
        if ( (scanf(" %c", Operation)) != 1 ) {
          return 1;
        }
    printf("\nInput another Number: ");
        if ((scanf("%lf", Num)) != 1) {
          return 1;
        }
    return 0;
}


double Arithmetic(double X, double Y, char op){
    switch (op){
        case '+':
            return (X+Y);
        
        case '-':
            return (X-Y);
            
        case '/':
            return (X/Y);
        
        case '*':
            return (X*Y);
            
    }
}
// // int NumChecker(int X){
// //     if (X==1){
// //         return (X);
// //     }else {
// //         printf("\nNot a Valid Number\n");
// //         // int X = scanf("%lf", &Result[0]);
// //     }
    
// }

int main(){
    
    int i=0;
    int state;
    double Result[100], Num[100];
    char Operation;
    
    while (1){
    printf("Input your Number: ");  
    scanf("%lf", &Result[0]);
    while (1){
    
        state = UserInput(&Operation, &Num[i]);
        if (state == 0 && Operation == '-'|| Operation =='+' || Operation =='/' || Operation =='*') {
         Result[i+1] = Arithmetic (Result[i], Num[i], Operation);
         printf ("\nResult: %.2lf\n", Result[i+1]);
         i++;
        }else {
            printf ("Invalid Operator or Number\n");
        }        
        
    }
    }      
    return 0;
}

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i just changed UserInput's return type to an int

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this way it would return 1 incase of invalid input, and 0 otherwise

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you could store this in a state variable to check if the input was valid or not

noble geyser Oct 21, 2022, 5:27 PM

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alright yeah so your way works

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but strangely it would still print out "Input Operation:" and "Input another Number:" before printing out the invalid message

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I tried to look for a way around that but came up short

mint rock Oct 21, 2022, 5:30 PM

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noble geyser but strangely it would still print out "Input Operation:" and "Input another Num...

hmm? lemme check

noble geyser Oct 21, 2022, 5:30 PM

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https://onlinegdb.com/Z3xX2eD80_

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Online GDB is online ide with compiler and debugger for C/C++. Code, Compiler, Run, Debug Share code nippets.

mint rock Oct 21, 2022, 5:30 PM

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oh yeah

noble geyser Oct 21, 2022, 5:32 PM

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other than that the calc's pretty much done

mint rock Oct 21, 2022, 5:35 PM

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noble geyser but strangely it would still print out "Input Operation:" and "Input another Num...

ah i found the reason

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probably

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checking the scanf return for the operator is useless

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because its a char, so it'll accept any input

noble geyser Oct 21, 2022, 5:37 PM

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mint rock checking the scanf return for the operator is useless

Yeah I alr removed that part

noble geyser Oct 21, 2022, 5:38 PM

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noble geyser https://onlinegdb.com/Z3xX2eD80_

Check this

mint rock Oct 21, 2022, 5:38 PM

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i fixed it

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too

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ah

noble geyser Oct 21, 2022, 5:38 PM

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How'd you fix it?

mint rock Oct 21, 2022, 5:38 PM

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that works too

mint rock Oct 21, 2022, 5:38 PM

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noble geyser How'd you fix it?

#include <stdio.h>

int UserInput(char* Operation, double* Num){
    printf("\nInput Operation: ");
        if ( (scanf(" %[+*-/]c", Operation)) != 1 ) {
          scanf("%*[^\n]");
          return 1;
        }
    printf("\nInput another Number: ");
        if ( (scanf("%lf", Num)) != 1 ) {
          scanf("%*[^\n]");
          return 1;
        }
    return 0;
}


double Arithmetic(double X, double Y, char op){
    switch (op){
        case '+':
            return (X+Y);
        
        case '-':
            return (X-Y);
            
        case '/':
            return (X/Y);
        
        case '*':
            return (X*Y);
            
    }
}
// // int NumChecker(int X){
// //     if (X==1){
// //         return (X);
// //     }else {
// //         printf("\nNot a Valid Number\n");
// //         // int X = scanf("%lf", &Result[0]);
// //     }
    
// }

int main(){
    
    int i=0;
    int state;
    double Result[100], Num[100];
    char Operation;
    
    while (1){
    printf("Input your Number: ");  
    scanf("%lf", &Result[0]);
    while (1){
    
        state = UserInput(&Operation, &Num[i]);

        if (state == 0 && Operation == '-'|| Operation =='+' || Operation =='/' || Operation =='*') {
         Result[i+1] = Arithmetic (Result[i], Num[i], Operation);
         printf ("\nResult: %.2lf\n", Result[i+1]);
         i++;
        } else {
            printf ("Invalid Operator or Number\n");
        }        
        
    }
    }      
    return 0;
}

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you can specify which values scanf should accept using []

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so i put all the operators in it

noble geyser Oct 21, 2022, 5:39 PM

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Omg my eyes

mint rock Oct 21, 2022, 5:39 PM

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the problem that i then ran into was because we use scanf

noble geyser Oct 21, 2022, 5:39 PM

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Screenshot_2022-10-22-00-39-35-658_com.discord.jpg

mint rock Oct 21, 2022, 5:39 PM

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if you use scanf, and it finds a non-matching character

mint rock Oct 21, 2022, 5:40 PM

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noble geyser

lmao why is discord doing that

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should be black on black

noble geyser Oct 21, 2022, 5:40 PM

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It's probably os side

mint rock Oct 21, 2022, 5:40 PM

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i guess

noble geyser Oct 21, 2022, 5:40 PM

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Whatever you did is out of my skill level rn

mint rock Oct 21, 2022, 5:40 PM

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i dont have an account on gdb so cant paste my code there lol

mint rock Oct 21, 2022, 5:40 PM

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noble geyser Whatever you did is out of my skill level rn

not really!

noble geyser Oct 21, 2022, 5:40 PM

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So it's not going to be what I submit in the end, though I appreciate the help

mint rock Oct 21, 2022, 5:40 PM

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only confusing part is scanf("%*[^\n]");

mint rock Oct 21, 2022, 5:40 PM

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noble geyser So it's not going to be what I submit in the end, though I appreciate the help

fair

noble geyser Oct 21, 2022, 5:40 PM

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mint rock not really!

No seriously I got a day to finish this

mint rock Oct 21, 2022, 5:41 PM

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you found a solution too

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so it worked out in the end

noble geyser Oct 21, 2022, 5:41 PM

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I can't be learning struct and flush or whatever

mint rock Oct 21, 2022, 5:41 PM

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oh the flush isnt needd

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i forgot to remove it

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but yeah i understand

noble geyser Oct 21, 2022, 5:41 PM

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mint rock so it worked out in the end

Yeah. Your original way makes sense to me i just don't get why it prints and asks for the operator and second number even if the first number is alr wrong. Doesn't really mess anything up though

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It's more of a "would be nice if it didn't"

mint rock Oct 21, 2022, 5:42 PM

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noble geyser Yeah. Your original way makes sense to me i just don't get why it prints and ask...

it does so because my way of checking for operator was seeing that if the scanf return was 1 or not

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but our operator is a char

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and char can accept all alphabets and numbers

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so it'll always return true

noble geyser Oct 21, 2022, 5:43 PM

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Wait so why did it still do stuff even after I removed it from the char scanf?

mint rock Oct 21, 2022, 5:43 PM

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so it only checked if the number was valid or not

mint rock Oct 21, 2022, 5:43 PM

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noble geyser Wait so why did it still do stuff even after I removed it from the char scanf?

?

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do you have that code

noble geyser Oct 21, 2022, 5:43 PM

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noble geyser https://onlinegdb.com/Z3xX2eD80_

It's this one

mint rock Oct 21, 2022, 5:45 PM

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noble geyser It's this one

oh

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same reason

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it doesnt check if operator is a valid operator

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as long as its a char

noble geyser Oct 21, 2022, 5:46 PM

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I'll check your solution tommorow, I alr have my laptop off

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And I don't think my 1 am brain is proeprly comprehending what you're trying to tell me

mint rock Oct 21, 2022, 5:46 PM

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okay!

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me neither, pretty late here

noble geyser Oct 21, 2022, 5:46 PM

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Thanks for the help.

mint rock Oct 21, 2022, 5:47 PM

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gnight!

carmine gustBOT Oct 21, 2022, 5:52 PM

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@noble geyser Has your question been resolved? If so, run !solved :)

carmine gustBOT Oct 22, 2022, 6:21 AM

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This question thread is being automatically closed. If your question is not answered feel free to bump the post or re-ask. Take a look at !howto ask for tips on improving your question.

#why doesn't it scanf a second time when I call the main() function?