View Compilation Error

0_0_19094104_11503.cpp: In function 'int main()':
0_0_19094104_11503.cpp:9:23: error: 'strlen' was not declared in this scope
     for(j=0;j<strlen(a)-1;j++)
                       ^
0_0_19094104_11503.cpp:17:23: error: 'strlen' was not declared in this scope
     for(i=0;i<strlen(a);i++)
                       ^