I have an issue after converted a float from a string, the result of my operation is null The NSLogs give the right value but vitesseMoyenne is equal to null -(void)setVitesseMoyenne:(float)uneDistanceTotale:(NSString*)unTempsTotal { //float tempEnFloat = [unTempsTotal floatValue]; NSLog(@"%@",unTempsTotal); float calculVitesseMoyenne = uneDistanceTotale / [unTempsTotal floatValue]; NSLog(@"%f",calculVitesseMoyenne); vitesseMoyenne = [NSString stringWithFormat:@"%f", calculVitesseMoyenne]; } Can you see what is wrong ?