matlab实现两个字符串数据相减

 代码分析：两个字符串可以是两个整数、两个小数或者一个小数一个整数的情况。在本代码中，将小数对齐后，直接去掉小数点，对空位进行补零操作，最后按位进行运算即可，比如'0.02' - '0.112'，则直接进行'0020' - '0112'的相减即可；'10'-'2'，则直接进行'10' - '02'的运算；'8'-'0.02'，则将'8'转成'8.0'，直接用小数减小数的函数即可。

function [result] = TwoStringSubstract(num1, num2) 
%% 两个字符串相减
    if ischar(num1) && ischar(num2)
        flag_fraction = IsFraction(num1, num2);
        % 两个小数相减
        if flag_fraction(1) && flag_fraction(2)         
            [result] = FractionSubFraction(num1, num2);
        % 一个整数减一个小数
        elseif ((~flag_fraction(1)) && (flag_fraction(2))) || ((flag_fraction(1)) && (~flag_fraction(2)))   
            % num1是整数字符串，num2是小数字符串
            if (~flag_fraction(1)) && (flag_fraction(2))
                [result] = IntSubFraction(num1, num2);
            end
            % num1是小数字符串，num2是整数字符串
            if (flag_fraction(1)) && (~flag_fraction(2))
                [result] = IntSubFraction(num2, num1);   
            end      
        % 两个整数相减
        else              
            [result] = IntSubInt(num1, num2);
        end
        
        % 用作最后确保结果的正负号无误
        if (str2num(num1) > str2num(num2)) && (result(1) == '-')
            result = RemovePos(result, 1);
        end
        if (str2num(num1) < str2num(num2)) && (result(1) ~= '-')
            result = ['-', result];
        end
    else
        disp("输入的数据不是字符串")
    end
end
%% 两个字符串数字相减的情况：整型-整型、小数-小数、小数-整数、整数-小数
% 通过三个函数来实现，IntSubInt()、FractionSubFraction()、IntSubFraction()
function [result] = IntSubInt(num1, num2)
    diff_bit_num = size(num1, 2) - size(num2, 2);
    if diff_bit_num ~= 0
        if diff_bit_num > 0
            [num2] = FillGap_front(num2, diff_bit_num);
        else
            [num1] = FillGap_front(num1, abs(diff_bit_num));
        end
    end
    bit_num = size(num1, 2);
    isless = isLess(num1, num2, bit_num);
    if (isless) 
        [result] = sub(num2, num1, bit_num);
        [result] = Insert(result, 0, '-');
    else 
        [result] = sub(num1, num2, bit_num);
    end  
end

function [result] = FractionSubFraction(num1, num2)
    [num1, num1_point_pos] = fraction2int(num1);
    [num2, num2_point_pos] = fraction2int(num2);   
    diff_point_pos = num1_point_pos - num2_point_pos;    
    if  diff_point_pos ~= 0
        if diff_point_pos > 0
            [num2] = FillGap_front(num2, diff_point_pos);
        else
            [num1] = FillGap_front(num1, abs(diff_point_pos));
        end  
    end
    diff_bit_num = size(num1, 2) - size(num2, 2);
    if  diff_bit_num ~= 0
        if diff_bit_num > 0
            [num2] = FillGap_back(num2, diff_bit_num);
        else
            [num1] = FillGap_back(num1, abs(diff_bit_num));
        end  
    end
    bit_num = size(num1, 2);
    [isless] = isLess(num1, num2, bit_num);
    if (isless) 
        [result] = sub(num2, num1, bit_num);
        [result] = Insert(result, max(num1_point_pos, num2_point_pos) - 1, '.');
        [result] = Insert(result, 0, '-');
    else 
        [result] = sub(num1, num2, bit_num);
        [result] = Insert(result, max(num1_point_pos, num2_point_pos) - 1, '.');
    end
end

function [result] = IntSubFraction(num1, num2)
    num1 = [num1, '.0'];
    [result] = FractionSubFraction(num1, num2);
end
%% 将小数变为整型，比如'0.005'->'0005'；'9.80'->'980'
function [a_, a_point_pos] = fraction2int(a)
    a_point_pos = SearchPointPos(a);
    a_ = RemovePos(a, a_point_pos);
end
%% 判断两个字符串是否是小数
function [result] = IsFraction(a, b)
    result = zeros(1, 2);
    result(1) = SearchPointPos(a);
    result(2) = SearchPointPos(b);
    if result(1) == -1
        result(1) = 0;
    end
    if result(2) == -1
        result(2) = 0;
    end
end
%% 将位数是bit_num的两个字符串整型数据a、b，相减得到的字符串整型的结果
function [result_] = sub(a, b, bit_num)
    result = []; borrow = 0;
    for k = 1 : bit_num
        i = bit_num - k + 1;
        j = bit_num - k + 1;

        x = a(i) - '0';
        y = b(j) - '0';    
        diff_xy = mod((x - borrow - y + 10), 10);
        
        result(end+1) = diff_xy;
        
        % 得到下一位被借走的数borrow
        if (x - borrow - y) < 0
            borrow = 1;
        else
            borrow = 0;
        end
    end
    
    % 调整result的顺序，将倒序变为顺序
    [~, result_col] = size(result);
    result_ = '';
    for i = 1 : result_col
        result_ = [result_, num2str(result(1, result_col - i + 1))];
    end
end
%% 调整两个整数的位数相同，不同的在前/后面补零，达到位数相同的效果
function [a] = FillGap_front(a, bit_num)
    % 在a前面补bit_num个零
    for i = 1 : bit_num
        a = ['0', a];
    end
end

function [a] = FillGap_back(a, bit_num)
    % 在a后面补bit_num个零
    for i = 1 : bit_num
        a = [a, '0'];
    end
end
%% 判断两个字符串整型数据，按位比较后，是否a row_str
        disp("输入的pos有误")
    else
        result = '';
        for i = 1 : row_str
            if pos == (i - 1)
                result = [result, ch];
            end
            result = [result, str(i)];
        end
        if pos == row_str 
            result = [result, ch];
        end
    end
end
%% 找到小数点在的位置
function [result] = SearchPointPos(a)
    result = -1;
    for i = 1 : size(a, 2)
        if (a(i) == '.')
            result = i;
            break;
        end
    end
end
%% 从字符串中剔除某一位
function [result] = RemovePos(a, pos)
    if (pos <= size(a, 2)) && (pos >= 1)
        result = '';
        for i = 1 : pos - 1
            result = [result, a(i)];
        end
        for i = pos + 1 : size(a, 2)
            result = [result, a(i)];
        end
    else
        disp("pos输入有误");
    end  
end