stdio.h   // printf, scanf, fopen, fclose, fprintf, fscanf, sprintf
stdlib.h  // abs, rand, RAND_MAX, srand, malloc, calloc, realloc, free, system, exit, atof, atoi, atol 
stdbool.h // bool, true, false
time.h    // clock, time, difftime, clock_t, time_t, CLOCKS_PER_SEC
math.h    // sin, cos, tan, asin, acos, atan, exp, log, log10, pow, sqrt, ceil, floor, fabs  
stdint.h  // int8_t, int16_t, int32_t, int64_t, uint8_t, uint16_t, uint32_t, uint64_t

string.h // 字符串
ctype.h  // 字符

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