View Compilation Error

0_0_21574562_9514.cpp:9:9: error: 'pair' does not name a type
 typedef pair<int,int> P;  
         ^
0_0_21574562_9514.cpp: In function 'int main()':
0_0_21574562_9514.cpp:17:29: error: 'scanf' was not declared in this scope
      while(~scanf("%s%s",a,b))  
                             ^
0_0_21574562_9514.cpp:19:24: error: 'strlen' was not declared in this scope
          int n=strlen(a);  
                        ^
0_0_21574562_9514.cpp:26:51: error: 'max' was not declared in this scope
             dp[i+1][j+1]=max(dp[i+1][j],dp[i][j+1]);  
                                                   ^
0_0_21574562_9514.cpp:27:25: error: 'writeln' was not declared in this scope
         writeln(dp[n][m]);  
                         ^