Lua和C中的数字表现异常

我用 Lua 和 C 编写了这个贪心算法程序。

Greedy = function(num)
local q = 0;
local d = 0;
local n = 0;
local p = 0;

local x = 1;

while x == 1 do
    if (num >= 0.25) then
        q = q + 1;
        num = num - 0.25;
        print("q");
    elseif (num >= 0.10) then
        d = d + 1;
        num = num - 0.10;
        print("d");
    elseif (num >= 0.05) then
        n = n + 1;
        num = num - 0.05;
        print("n");
    elseif (num >= 0.01) then
        p = p + 1;
        num = num - 0.01;
        print("p");
    end

    if (num == 0) then
        x = 0;
    end
end

if (x == 0) then
    local all = q+d+n+p;
    print(all);
end

end

 Greedy(1);

这段代码对于一些数字可以正确工作，但是如果我尝试计算像 0.90、0.04 或 0.12 这样的数字，它就无法正常工作。我还用 C 编写了相同的代码，但是我遇到了同样的问题。

#include <stdio.h>

int greedy(void){
    int quarter = 0;
    int dime = 0;
    int nickel = 0;
    int penny = 0;

float num = 0.40;

int x = 1;

while(x == 1){
     if (num >= 0.25){
         quarter = quarter + 1;
         num = num - 0.25;
         printf("q\n");
     }else if(num >= 0.10){
         dime = dime + 1;
         num = num - 0.10;
         printf("d\n");
     }else if(num >= 0.05){
         nickel = nickel + 1;
         num = num - 0.05;
         printf("n\n");
     }else if(num >= 0.01){
         penny = penny + 1;
         num = num - 0.01;
         printf("p\n");
     };

     if(num == 0){
         x = 0;
     };
};

if(x == 0){
    int all = quarter + dime + nickel + penny;
    printf("%i\n", all);
};
return 0;
};

int main(void){
   greedy();
}

我做错了什么？