可以使用库函数
C++:

#include <cstdio>
#include <cmath>
float n, out;
int main() {
	scanf("%f", &n);
	out = fabsf(n);
	printf("%.2f", out);
	
	return 0;
}

Python:

from math import fabs
n = float(input())
out = "{:.2f}".format(fabs(n))
print(out)