To use a given graphic package I need to define, book and fill histogram. How can I get the name of the histogram which is a string to concatenate with 2 integer as a string ( hts_i_j ) in 3 for loop instead. That has to be done in c++ See the exemple below to define TH1F* hts_5_53; TH1F* hts_5_54; …… TH1F* hts_5_69; to book hts_5_53= HDir.make("hts_5_53")," Title", 100,0.,100.); hts_5_54-HDir.make("hts_5_54")," Title", 100,0.,100.); …… hts_16_69-HDir.make("hts_16_69")," Title", 100,0.,100.); to fill hts_5_53-Fill(f) hts_5_54-Fill(f) …… hts_16_69-Fill(f) Instead I would like to define, book and fill in 3 for loops. e.g . for(int i=5, i<17, ++i){ for(int j=53, j<70, ++j){ hts_i_j } } how can I get the string hts to concatenate with the indices ( i,j) in a simple short way while defining, booking and filling in 3 for loop instead