need help with finding errors

Code:

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//question 1
int main()
{
int choice = -1, num1,num2,trials = 0;


//give the user a max of five trials
while((choice = -1) && trials <5)
{
    printf("Enter a number : ");
    scanf("%d",&num1);
    printf("Enter another number: ");
    scanf("%d",&num2);
    printf("Their sum is %d\n",(num1+num2));
    printf("Enter -1 to repeat, 1 to exit");
    scanf("%d",&choice);
    trials++;
}
    return 0;
}


   
   
   
//question 2
int a = -75;


if(a != 0)
{
    printf("The number is different from 0\n");
    printf("Please enter another number \n");
}
else if (a<0)
    printf("The number is negative \n");
else
    printf("The number is positive \n");

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There are 2 questions, as I posted in the above.
The question says there is one error in each questions.
I tried to find errors but, I couldn't find any....
I even tried to run the program and it worked fine.
Could anyone help me with finding errors?

For the first one, try exiting the program early. For the second one, try to obtain the output "The number is negative \n".

Thank you very much for your help!!!
I think I found errors...
For the first one, there is no statement to exit the program and for the second one, there is "else if" instead of "if".

Code:

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while((choice = -1) && trials <5)

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Note that = is an assignment, not a comparison.