Question

What is the use of width in the printf() statement? Why is the output 7 in the example below?

Code

int add(int x, int y)
{
    return printf("%*c%*c",  x, '\r',  y, '\r');
}

int main()
{
    printf("Sum = %d", add(3, 4));
    return 0;
}

Output

Sum = 7

Answer 1

printf returns the number of characters output. %*c means print a character and pad to the width specified by an argument. So printf("%*c", 3, '\r') means to print a carriage return with 2 spaces before it. printf("%*c%*c", n, '\r', m, '\r') therefore prints n + m characters – that’s n – 1 spaces to pad the first \r, m – 1 spaces to pad the second \r, and the two carriage returns. That’s why it returns 7.

A carriage return takes you back to the start of the line, so after printing those n + m characters the next thing printed will appear at the start of the line. That means "Sum = " overwrites the output of the first printf.