View Compilation Error

0_0_28318566_12576.cpp: In function 'int main()':
0_0_28318566_12576.cpp:20:25: error: 'strlen' was not declared in this scope
   for(int j=0;j<strlen(a);j++)  //找最小元素
                         ^
0_0_28318566_12576.cpp:33:25: error: 'strlen' was not declared in this scope
   for(int k=0;k<strlen(a);k++)
                         ^