To find the first digit of a number in C, you can use a combination of mathematical operations and control flow statements. Here is one way you can accomplish this:

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int firstDigit(int n) {    while (n >= 10) {        n /= 10;    }    return n; }

This function takes an integer as an argument and uses a while loop to repeatedly divide the number by 10 until it is less than 10. The first digit of the number will be the last value of n before the while loop exits.

You could also use the modulus operator % to get the last digit and then divide the number by 10 until the number is less than 10

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int firstDigit(int n) {    if(n<0) n = -n;    while (n >= 10) {        n /= 10;    }    return n; }

This function first checks for negative numbers and make them positive, so the result is always positive, and it uses a while loop to repeatedly divide the number by 10 until it is less than 10. The first digit of the number will be the last value of n before the while loop exits.

This function assumes that the input number is always a positive number. If the input number can be negative, it's important to handle this case before the while loop.