Why are the outputs different in C?

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C

#include<stdio.h>
void main()
{ 
    int a=010;
    printf("\na=%d",a);
}

#include<stdio.h>
void main()
{ 
    int a=010;
    printf("\na=%o",a);
}

#include<stdio.h>
void main()
{
    int a=010;
    printf("\na=%x",a);
}

Output for first program:8
Output for second program:10
Output for the third program:8

Since I am a beginner, I would like to know the reason behind the difference in ouput when using different letters after % in printf(). The next I don't understand how the number in the variable doesn't print and other values get printed.

I don't understand how 010=8 for octal when it is equal to 2 in binary.
Please help me. Thanks.