#include<stdio.h>
void main()
{
    int a,b;
    float sum,minus,product,quotient,remainder;
    scanf("%d%d",&a,&b);
    sum=float(a)+b;
    minus=a-b;
    product=a*b;
    quotient=a/b;
    remainder=a%b;
    printf("%.2f\n%.2f\n%.2f\n%.2f\n%.2f\n",sum,minus,product,quotient,remainder);

}

强制类型转换用(float)a

把float（a）改成 a 就可以了

#include <stdio.h>
void main()
{
    int a,b;
    float sum,minus,product,quotient,remainder;
    scanf("%d %d",&a,&b);
    sum=a+b;
    minus=a-b;
    product=a*b;
    quotient=(float)(a)/b;
    remainder=a%b;
    printf("%.2f\n%.2f\n%.2f\n%.2f\n%.2f\n",sum,minus,product,quotient,remainder);
}