2025-08-18 20:01:21

content/en/notes/coding/cheat_sheet/c/index.md

@@ -2,4 +2,54 @@
 title = 'C'
 date = 2024-09-20T04:17:50Z
 draft = false
-+++
++++
+
+<!-- 笔试题有的时候不给正常输入，只给plain text -->
+## Format Specifier
+
+Common specifiers:
+```
+%d      int
+%u      unsigned int
+%c      char
+%s      string (char s[])
+%p      void*
+%ld     long
+%lld    long long (64bits)
+%f      float/double
+%lf     float/double(usually used in scanf)
+```
+We can extend the format specifiers:
+``` C
+printf("%5d", 33);       // width      "   33"   
+printf("%.2f", 3.14159); // precision  "3.14"
+printf("%8.2f", 3.14159);// "    3.14"
+printf("%-5d", 33);      //Alignment   "33   "
+```
+
+## IO
+Read or print via terminal:
+
+``` C
+int x;
+scanf("%d", &x);
+printf("%d", x);
+```
+
+
+## Type Conversion
+String to int, float....
+``` c
+int i = atoi("123");
+double d = atof("3.14");
+
+long l = strtol("123", NULL, 10);  // safer, auto detec errors
+double d2 = strtod("3.14", NULL);
+```
+
+Numbers to string:
+``` c
+int i = 123;
+char buf[20];
+sprintf(buf, "%d", i); 
+```