Why is my compiler not showing an error when I'm using '=' instead of '==' in an 'if' conditional statement?

I am a beginner in C programming and was practicing a program to find the greatest numbers among 10 number using arrays.

So, in the first program, the compiler is issuing a warning:

warning: suggest parentheses around assignment used as truth value [-Wparentheses]|

But it is not an error, which means that the program is running, but always the number that I input is being shown as the greatest number.

The second one is running just fine and is showing correct output. Why is the compiler only showing me a warning in the first program, but not showing an error?

I think that there isn't any such operator as '=', so in my case the code mustn't run, but why is there only a warning, not an error?

The first program:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int x, i;
    float a [10];
    printf("Enter 10 numbers: ");

    for (i = 0; i <= 9; i++)
    {
        scanf("%f", &a[i]);
    }

    for (i =0; i <= 9; i++)
    {
        x = 0;
        for (int j = 0; j <= 9; j++)
        {
            if (a[i] > a[j])
            {
                x++;
            }
        }

        if (x = 9)
        {
            printf("The greatest number is %f", a[i]);
            break;
        }
    }
}

The second program:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int x, i;
    float a [10];
    printf("Enter 10 numbers: ");

    for (i = 0; i <= 9; i++)
    {
        scanf("%f", &a[i]);
    }

    for (i = 0; i <= 9; i++)
    {
        x = 0;
        for (int j = 0; j <= 9; j++)
        {
            if (a[i]>a[j])
            {
                x++;
            }
        }

        if (x == 9) // Replaced '=' in the first program with '=='
        {
            printf("The greatest number is %f", a[i]);
            break;
        }
    }
}

Note: I am using Code::Blocks and the MinGW compiler

It's not an error, = is the assignment operator, you are allowed to use the assigment operator inside an if statement.

Since it's not a common use, the compiler warns you, to verify if that is indeed what you want to do, it's not mandated to do it, but it's a safety feature.

An assignment like that, inside an if statement will always be true, except if the assigned value is 0 in which case te condition will evaluate to false.

Note that if you want to treat warnings as errors you can use -Werror flag, in fact I think it's a good idea to do so.