Add + and - operators

main.c

@@ -7,9 +7,29 @@ int main(int argc, char **argv) {
     return 1;
   }
 
+  char *p = argv[1];
+
   printf("  .globl main\n");
   printf("main:\n");
-  printf("  mov $%d, %%rax\n", atoi(argv[1]));
+  printf("  mov $%ld, %%rax\n", strtol(p, &p, 10));
+
+  while (*p) {
+    if (*p == '+') {
+      p++;
+      printf("  add $%ld, %%rax\n", strtol(p, &p, 10));
+      continue;
+    }
+
+    if (*p == '-') {
+      p++;
+      printf("  sub $%ld, %%rax\n", strtol(p, &p, 10));
+      continue;
+    }
+
+    fprintf(stderr, "unexpected character: '%c'\n", *p);
+    return 1;
+  }
+
   printf("  ret\n");
   return 0;
 }

test.sh

@@ -18,5 +18,6 @@ assert() {
 
 assert 0 0
 assert 42 42
+assert 21 '5+20-4'
 
 echo OK