C function still INVALID number [closed] - c

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#include <stdio.h>
int main() {
/*function declaration*/
double invalidInput(double);
int loop_obeTask;
double obe_Task[3];
double checkInput ;
for(loop_obeTask = 1 ; loop_obeTask < 4 ; loop_obeTask++)
{
printf("OBE%d : ", loop_obeTask);
scanf("%lf",&obe_Task[loop_obeTask]);
checkInput = invalidInput(obe_Task[loop_obeTask]);
if(checkInput = 1)
{
printf("INVALID INPUT \n" );
break;
}
}
return 0;
}
double invalidInput(double inputGrade)
{
double indicator;
if(inputGrade > 100)
{
indicator = 1;
}
else{
indicator = 0;
}
return indicator;
}
Hello Guys, want to validate the input numbers using the function once the user enters > 100 IT IS INVALID INPUT but in my case, it always shows invalid input both greater and less than 100. I can't post image because my reputation less than 10.
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Answer 1

Short answer
You're not checking the value, but assigning it: if(checkInput = 1)
You should use the == operator instead.
Long answer
Even if it does compile, your code presents numerous conceptual mistakes:
You're using double as return value of invalidInput(). Since that function is for validation only and it returns either 1 or 0, you should use int as return type instead.
Your for loop starts at index number 1, which is wrong and will lead to undefined behaviour. C array indexes starts at 0, so if you define an array with size 3, the available indexes are going to be 0, 1, 2, and the loop should look something like for (index = 0; index < MAX; index++) where MAX is 3 in this case.
Your if condition is not checking the equality of checkInput and 1. That's because you're using the assignment operator =, instead of the equality operator ==.
It's common practice to put your function declarations at the top of your file and before the main definition, both for readability and scope reasons.