Question

i have doubt im a new learner of c in some sentence we use( "%d",a) in scanf and sometimes in printf how do you find it?

Answer 1

Could you expain your question further and give an example? Also the scanf you used should be ("%d, &a");

Answer 2

scanf() scans the standard input for a specific pattern. The pattern is provided in quotes. In your case, it is "%d", which means a decimal integer. Then it is stored at a given variable, to be precise, stored at the address of a given variable. You can get the address of the variable via the & operator, hence you have a & before your variables in scanf().

printf() prints to the standard output. It also uses a format specifier, similar to scanf(). However, you are printing a number here, so the compiler is not interested in the memory address of the variable, but the actual value stored in that variable (on that memory address), hence with printf() you do not use the & (memory address of) operator.

#include <stdio.h>

int main()
{
    int number;
    printf("Please, enter an integral number: ");
    scanf("%d", &number);
    printf("You entered: %d\n", number);

    return 0;
}

I hope this makes more sense now. Have fun learning!