feat: add more user programs

1 files changed, 78 insertions, 0 deletions

diff --git a/user/calc.c b/user/calc.c
new file mode 100644
index 0000000..2d0e3f8
--- /dev/null
+++ b/user/calc.c
@@ -0,0 +1,78 @@
+#include "user.h"
+
+static int is_digit(char character)
+{
+    return character >= '0' && character <= '9';
+}
+
+void _start(void)
+{
+    put("calc, e.g. 3 + 4 * 2 (left to right), empty line quits\n");
+
+    char line[128];
+    for (;;)
+    {
+        put("> ");
+        int length = read_line(line, 128);
+        put("\n");
+        if (length == 0)
+            break;
+
+        long accumulator = 0;
+        char operator = '+';
+        int valid = 1;
+        int saw_number = 0;
+        int position = 0;
+        while (position < length)
+        {
+            char character = line[position];
+            if (character == ' ')
+            {
+                position++;
+                continue;
+            }
+            if (is_digit(character))
+            {
+                long value = 0;
+                while (position < length && is_digit(line[position]))
+                    value = value * 10 + (line[position++] - '0');
+                if (operator == '+')
+                    accumulator += value;
+                else if (operator == '-')
+                    accumulator -= value;
+                else if (operator == '*')
+                    accumulator *= value;
+                else if (operator == '/' || operator == '%')
+                {
+                    if (value == 0)
+                    {
+                        put("divide by zero\n");
+                        valid = 0;
+                        break;
+                    }
+                    accumulator = (operator == '/') ? accumulator / value : accumulator % value;
+                }
+                saw_number = 1;
+            }
+            else if (character == '+' || character == '-' || character == '*'
+                     || character == '/' || character == '%')
+            {
+                operator = character;
+                position++;
+            }
+            else
+            {
+                put("bad character\n");
+                valid = 0;
+                break;
+            }
+        }
+        if (valid && saw_number)
+        {
+            put("= ");
+            put_int(accumulator);
+            put("\n");
+        }
+    }
+    sys_exit(0);
+}